I'm sure someone has done it, and logically, it should work fine. A spring really doesn't know if it's supporting a trailer or the front of a rod. But I would question the economics of doing it versus just buying a Speedway spring and shackles. How much difference is there in cost? I also wonder if 3 leaves are enough, even though the capacity shows 1000. Most hot rod springs are 4-5 leaves.

I like making stuff too, and modifying things, but sometimes it just makes sense to buy the parts that are made specifically to do a job and be done with it.

Don