If your battery cables are hot the resistance is to high in the cables or it is pulling a very high number of amps. What size and length cable did you use? Check again for a good ground.

Pull the coil wire and see if it turns any easier

1) As mentioned, check gauge of starter cables. That could be a problem.
2) There should be a ground cable from the block to the chassis. Make sure this is good and big enough. You might want to connect a cable between one of the starter bolts and chassis. If you're using engine plates that directly bolt to the frame and engine you can skip this step!
3) If the timing is to far advanced the engine will be hard to turn. Try cutting back the timing a little with the distrubutor and see if it turns easier -- you can do this while it's cranking. It won't hurt to break the engine in with the timing retarded a bit.
4) It's more likely that the bearings are tight than the rings. Did you check bearing clearances w/plastigage? I didn't once, and it turned out that the bearings were tight.
5) Did you "prime" the carb? Pour about 1/4 cup of gas down the carb then start. Make sure the air filter is on and don't stand over it. An open carb and a back-fire could torch the hood insulation, that's why I say put the air filter back on after doing this. Any time I've started a car it's had a little gas trickeld down the carb first, even if it was just run out of gas. Works every time! If it fires but doesn't start, do it again. Might take 2-3 times pouring a little gas down the carb to get it started. I'd do that rather than use starting fluid.

I hard a hard time gettng a flat head six to start a long time ago. Luckily it was a stick and I lived on a farm at the time. Dragging it down the road for 200-300 feet in second gear with the tractor did the trick! Make sure you have a 30' or longer tow strap/chain, don't want to hit the tractor when it starts!

Turns with no plugs, won't with plugs?
My 2 cents, check the cam, sounds like it's 180 degrees out.

Mystery solved - I'm an idiot.

I double checked the timing and found that on the compression stroke the distributor was out 180 degrees, which means I screwed up on the timing gear.

I tore down the timing case and guess what, it's true I am an idiot.

Correcting the timing gear orientation in the morning and expect it to start right up.

I'll let you know how it goes.

Thanks for all the shared wisdom and great stories, I learned a lot.

I know better, thought I had double checked but must have rotated the crank once before I set the gears - crap - two days wasted on the project but lots of great info from you guys.

Thanks again.

The cam can't be 180 out, but what you did solved the problem, next time just turn the distributor 180 degrees instead.

Actually a cam can be out, I wasn't sure what engine he was working on, some older engines like the Y block Ford line up with the timing marks at 3:00 and 3:00 while others are 6:00 cam and 12:00 crank.

I've always heard it called 180 out since each is off by 90 degrees if you put the 3-3 engine at 12-6, but then there are a lot of old slang terms that aren't really acurate sayings.

But at least he found the problem.

The cam can not be 180 out, it is a 2 to 1 ratio to the crank so after 1 turn it would be where you should have originally set it up. The distributor can however be 180 out and this is what your issue was.

Not really wanting to get into a debate on semantics, but here is what I was referring to.
Only way I knew this was I rebuilt several Y blocks years ago and my old Auto shop teacher referred to it as being 180 out. But I found this on the web just now.
Again, not trying to be smart, just explaining my (slang) 180 degree statement.

[Ford Y-blocks use an unusual location for the timing marks when installing the timing chain. The timing marks are located 12 pins apart on the left side of the engine. Most Y-block timing chains have identification marks on links that are 12 pins apart.

First step in installing the timing chain and gears is to check the spacer ring; be sure the chamfer side is toward the cam. Next, install the woodruff keys in the crank and cam. Now slide the crank gear on the crank and position the timing mark by turning the crank, to the 3:00 o'clock position. Install the cam gear and position the timing mark on it at 3:00 o'clock. Now remove both gears. Place both gears in the timing chain with the timing marks 12 pins apart. Start the crank gear on the crank. As you slide the crank gear down, start the cam gear over the cam. Line up and engage the cam gear keyway with the key on the cam first. This will slow you to turn the cam so you can engage the key in the keyway on the crank. When both gears are installed, count the pins between the timing marks. There has to be 12 pins between them.]

Also at this site. http://www.ford-y-block.com/assembly errors.htm

[Timing gear installation. Some people try to align the timing marks on the gears toward each other as is common on newer engines. This is bound to happen more often now as the replacement timing chains no longer have the pins marked for correct alignment with the gears. The marks on the Y-Block timing gears aim toward the oil filter side with 12 pins between them.]

Who knows, maybe this will help someone else as some of this old stuff gets forgotten.

OK, so I have heard from lots of folks. I got some really good advice. I began to doubt what I had done.

So... I pulled the timing cover (and all the crap that involves) and double checked.

I had done it right - dots facing each other dist pointing to number one etc...

So I wasn't an idiot about the timing assembly after all.

I put it all back again and checked all three ground points, sanding off any paint to provide a clear clean contact point metal to metal.

This added a half a groan when I tried it again.

I was about to kick and throw the battery (which had been recharged) when I noticed the cranking amps spec on the battery sticker.

I bought this car used with 71,000 miles on it. The guy who had it before me cheaped out and had a 350 amp battery in the car.

I checked the battery specs at the store and found that new, this car should have an 875 amp battery.

I hooked up the new battery and it started in about 2 seconds. Runs great!

This experience has taught me a lot including some electricity theory.

(Get a BIGGER battery).

Thanks to all who responded, and to those of you who suspected the battery - YOU WERE RIGHT!

Mistakes are all about learning -- you gained a lot of experience with one tiny problem. Looking at ti that way this becomes a positive experience.

We've all made stupid mistakes. Even the most experienced engine builder has (and will!) make them. Getting a distributor 180 out is oh so easy to do! Well, double checking didn't hurt, even though the timing gear/chain assembly wasn't out, and apparently the distributor was correct also. I think I'd have checked everything else before coming back to the battery myself, knowing I had a good battery.

Good luck.