Late 80's Camaros/Firebirds are 62" wide from mount surface to mount surface. The IROC-z's came with posi/disc in 3.08, 3.42 and 3.73 with the 3.08 the most common. Not familiar with the mounting width of your year truck but they are a 5 on 4-3/4 lug pattern and front disc conversions are available in that size from most vendors.
The diffs are from behind the 2.8 V6 with automatic transmissions. They're a great conversion into AD's and hopefully the earlier trucks....plentiful, relatively lower mileage and cheap. If 62" will work, it's another option.
Dave
