[Classic Heartbeat]

The 3/4 ton frames are heavier than the 1/2 ton frames by about .050" and also the rear cab mounts are lower. I do not know anyone who is making 3/4ton drop spindles that keep the wheels 8 lug. There are 3/4ton drop spindles however they require you to change to 5 or 6 lug because they use the 1 1/4" spindle pin. As for the rear end, the easiest thing would be to find one out of another 67-72 3/4 ton truck. If you have rear trailing arms, 73 and newer didn't use them. If you have rear leafs the frames are wider so the spring pearches are farther apart. Lot of other things that need to be addresses, but there isn't enough information in your innitial post to address them. WES