The 258 and 232 have a common block casting number. They are machined exactly the same way, year for year. There is a number stamped on a boss near the distributor that gives the engine size, A or E is the difference. Over the years, the parts could have been swapped around during a rebuild. The only way to be sure it's a 258 is to measure the stroke. A 258 has a 3.88" (3-7/8") stroke, a 232 has a 3.5" (3-1/2") stroke.

If your buddies Scout 's 232 block and head are good, simply install a 258 crank and rods and you will have a 258!
The '72-'80 crank is fully counterweighted and is smoother running than the lighter '81-'90 crank. The later crank has a shorter front snout but will still work with the early pullys/damper. The '70-'71 258 crank is only useable with a stick or Borg Warner automatic, but is fully counterweighted, too.

Personally, I would consider installing a later 4.0l or 4.6l stroker combo (.030" over 4.0l block and head with a 258 crank) with '91-'95 Mopar EFI. The driveability improvement, power output and torque will make a world of difference over the old 232 and probably give better fuel economy, too. CJOffroad.com has an excellent 4.0l swapping forum with all the help you would need to adapt the EFI from a Cherokee, Grand Cherokee or Wrangler to your earlier vehicle.

Hope this helps!