Where I'm really stumped is the front end.
If you're swapping in a car rearend with the five lug pattern, your straight axle options for the front would be to swap in a 1/2 ton axle and get a 5 lug disc brake kit, or 5 lug drums/hubs with passenger car parts, or fit up 1/2 ton spindles to your 3/4 ton I-beam to use the 5 lug disc brake kit.
