This is my nightmare! Anybody need a 307 crank in good condition? Also does anyone out there know a 307 by looks? How about silver and blue engine where everything checks like a 350 except the crank is a 307. The oil filler neck is long and on the drivers side of the engine. This block was sold to me as a 350 chevrolet. Now it does have the Mexico markings that the early chevrolet engines had.
A chevrolet dealership in my town told me that you cannot get any information on the early engines from GM.

For '68 Chevrolet released a larger low-performance 307 engine as a replacement for the 283. The 307 used a 283 bore and a 327 stroke (3.875-inch bore and a 3.25-inch stroke). Production of the 307 ran until '73.

if it has a 4'' bore like a 350 then you have a 327 and you can build it as a 350 383 etc

I don`t know of any "early markings" chevy mexico engines. The only ones I know of are Target Master replacement engines from GM, these were made in Mexico, and on the rear of the block by the casting number they say "hecho en mexico" which means made in mexico. There could have been early chevy engines made in mexico, but in my years I never seen one. The only target masters I know of are all 350`s, I never heard of or seen a 327 mexico engine. whats the cranks casting numbers? What`s the suffix code on the block? the suffix code is on the passengers side front block deck pad. What`s the blocks casting numbers? Have you measured the bore of the block?

The casting number is on the left rear of the block, on top, right behind where the cylinder head goes. Most likely 7 digits, but 6 or 8 would be OK. Take the number to http://www.mortec.com/castnum.htm and see what it is. Sometimes the numbers are a bit hard to read, since they're kinda crudely cast, so be open-minded. 3's look like 8's, etc.

350 pistons would ride ~1/8" too low if they were hooked to a 307 crank. Somebody musta been smokin loco weed in the shop that day, and it sounds like you lucked-out and got sold the mis-matched engine. Pistons designed for a 327 engine (compression height 1.675") would make it right. Chevy, in fact, did this exact combo in '68 & '69 in low-performance Camaros & Impalas with 2-bbl carbs, but they ran right nicely with a few appropriate bolt-ons.

Hey Gideon,it looks like they are all valid answers.You ever figure out which engine to build (302,283,327)?If it was me and I could make it work in my budget,I would get a 350 crank and be done with it.Hopefully you will be able to sell the 307 crank(large journal 327 )and recoup some cash.

Try this too, If you have the heads off, just measure the cylinder in the block. If it is 327 or 350 it's 4" dia. If it is 283 or 307, it's 3.87" dia.
If it is 3.25 stroke it's either 3.87" for 307 or if it's 4" dia. it's 327.
If the stroke is 3 & 1/2" or more exact 3.48" with a 4"dia. it's a 350cid.
If it's less then 3.87" dia. or close with a 3.48" stroke then you have a 305.
Hope this helps

the first engine i ever built was a 327 crank (forged steel large journal crank) in a 350 with 350 pistons. i was only 19 & the crank was sold to me as a 350 steel crank. i didn't know the difference. it had 1/8 deck height. believe it or not that thing was a beast for what it was. headers, victor jr intake, 750 edelbrock, 292 comp cams cam, 186 1.94 valved heads, 3.73 gears & a 3,000 stall. i know it lost a bunch of ponies to the 7.10 compression, but it would scream. smoked a lot of 350s with it & gt mustangs too.

if this is what you have put the right crank or pistons in it. if the heads are off just rotate the engine & see what kind of deck height you have. you can see if the piston stops 1/8" down in the bore.

That is funny what you did. You just happen to build a motor for a supercharger. It would make a lot horse power.

i would have like to had a big 6-71 sitting on top of it.