Hi and welcome to the site! The late 60s C10 trucks were great for the AD pickups. Just the right width. Many of those had ratios starting at 3:07 (which is what I have). Mine was out of a 1969 C10 which had been a really nice truck before somebody decided to drive it upside down. You can even use the same emergency brake setup simply by modifying things a wee bit. If by chance you're swapping the transmission to the T5 look for the T5 which has the gear chain beginning with 4.03 and you'll have an overall first gear ratio of 12.08 and that will let you still use your pickup as a genuine pickup (the first 3 gears will feel exactly like the original setup) plus drive at 60 mph at around 2000 rpm, 65 at 2100 rpm, etc. You'll need to cut off the coil spring mounts the late 60s C10 trucks came with, discard the panhard bar, smooth the axle and use any generic spring perch piece (or you can use the round adjustable collar like I did and weld when you get your pinion angle correct. You'll even get to use the same brake line hookup and wheels. When you're welding those perches, just use common sense and weld 1/2 inch or so on one side then move to the other side while it cools, return and keep that up so you don't risk warping the housing (which I've seen people do by just running a solid bead). Easy work if you can find one. Good luck!
