The stock length on a tri five rear end is 59-5/8. You should always measure from end to end where the wheel bolts on, not the backing plates. If you measure from the backing plate, depending on the width of the rear brake shoes, you will get a different measurement.

Same width as classic are---66-67 Chevelle, 67-81 Camaro, 68-76 Nova. 2 3/4 inches narrower than a classic---65-67 Chevy 2/Nova----About 1 1/4 inches wider than a classic---68-72 Chevelle, 70-72 Monte Carlo. This is what I have in my notes. I'm pretty sure they are close to accurate. Other rear ends in same body group could work also. Good Luck

S-10 2x4 rearends are around 53 inches overall. 4x4 rearends measure out about 58 inches. The 96 and up 4.3 S-10's have the 8.5 inch 10 bolt, or so I have been told. Measure before you spend $$. I like to set up the wheels I plan to run and measure between and go from there. Just hate it when wheels don't set right.

more info regarding '57-'64 Olds/Pontiac rear ends.

• '57 Pontiac rear end will bolt into '55-'57 Chevys. ('55-'56 Pontiac rear end will also bolt in, but is different design than stronger '57-'64 units). Later '59-up years are wider (unsure about '58).
• '57 Olds rear end is same width as '57 Pontiac & '57 Chevy, but used coil springs and requires welding on 2" wide leaf spring perches to fit into '55-'57 Chevy. Later '59-up years are wider (unsure about '58).
• '57-'64 Olds and Pontiac 3rd members are interchangeable between '57-'64 Olds/Pontiac rear end housings.
• Pontiacs had 29-spline axles; Oldsmobiles had 31-spline axles. To fit stronger 31-spline axles into Pontiac housing:
  1. Either use Olds 3rd member or fit Olds 31-spline spider gears to Pontiac 3rd member.
  2. Either use same-length Olds axles in Pontiac rear end housing or have custom 31-spline aftermarket axles made.
  3. Another option would be to use either stock or aftermarket axles for 31-spline 9" Ford and weld Ford housing ends onto Olds/Pontiac housing. This would give more options for fitting rear disc or drum brakes, as kits for 9" Ford would now bolt on. Later (wider) Olds/Pontiac rear housings could be narrowed to fit when Ford housing ends welded on. (Currie Ent. and other companies stock several different Ford housing ends.)
• Jason, your notes on the '57-64 Olds/Pont rears aren't completely accurate, for instance the spline count was 29 for both '57-8 Olds and Pontiac, while 31-spline was for '59-64 Olds and Pontiac. The difference was between the first 2 years and the other 6 years, not between Olds and Pontiac.