Lance use 73-87 3/4 ton drop spindles, the 71-72 and 73-87 3/4 ton spindles are the same, you'll need to use tie rods and ball joints for 71up to install then use 71-87 rotors, calipers & bearings.
We haven't put these together as kits yet for 67-70's but you will find the drop spindles here in our online catalog
http://www.gmcpauls.com/73-91_d&s.htm
We can also have drop springs custom made for your 3/4 ton if it has trailing arms, contact us if interested.
GMCPaul