I am going to go out on a limb, but if your truck is a 1950 1/2 ton, you do NOT have an original rear end if it is open driveshaft. Also, the original rear end is closer to the width of the s-10 4wd. The non-original rear end you have under your truck is "too" wide. Nothing wrong with what you got. And I can't help you with the 283 PG swap.

Always get a 2nd opinion, especially if I am the source of the 1st opinion.