Consider the differential swap. This would be the easiest way to success with. You will keep the brake lines and emergency brakes as they are. No mods. You will not get disc brakes but the diff will be 3.90. You will have to mod the axle perches as the pivots will not work. As 52carl noted, the T5 is best option and closest to bolt in you will get with minimal modifications. They are getting hard to find used but new and rebuilt’s are available. This is the route I went with no regrets.
