I have my car stashed at the in-laws house right now so I can't go look at the tires. I think they are 275-65-R15s, but I could be wrong. They physically measure 27' tall and are about 10" wide.
I used the 8" rearend out of my old Maverick. The Maverick rearend is about 1/2" narrower than the Ranchero rear. I had to get new brackets to bolt the leaf springs to the rear because on the Maverick there are staggered shocks. One that mounts to the front and one that mount to the rear. The Ranchero's shocks are both in front. I got the new plates from a 60's Mustang.
I had to cut the wheel wells a little in front of the wheels. If you look at the wheel well you can see how the wheels will hit with a taller tire. I cut them from where the well meets the cab of the car and made a nice radius clear of the tire up to where the rest of the wheel well comes around. Some people make a template of the rear half and copy it for the front. I haven't tried that, but it would probably work. It makes your rear wheel well look like the front.
Then, there is a 90o lip at the bottom of the wheel well. I folded in up and in so that I could get the extra 1/2" clearance width wise. I used a torch and 2- 5 lb. mallets to do that.
The e-brake hooked up the same as the stock rearend. I had to get a new soft brakeline for the 8" rear that would hook up to the existing hard brakelines. I went to Kragens and matched up the fittings with one that worked. The stock fittings are smaller on one end.
I used the C4 tranny out of the Maverick and I used the driveline from the Maverick also.