I had a friend with an 84 and what I think was a trailmaster lift...
Now maybe he installed them wrong, but the shackle was pulled way forward to where it was the only way it could be bolted on the truck... It was at a 45 with the low left the spring and upper right the frame, like the spring was a good 4 to 6" shorter than it needed to be... It was totally backwards than any shackle I've ever seen.
It lifted it... And I don't own it so I don't know if it settled or not, but I highly doubt it considering the angle... But ever since I saw that and a el-cheapo lifted Chevy about the same way, I gave up on cheap spring lifts...
Rears up front, AllPro, Marlin or OME... save yourself the trouble of buying junk.