I expect the ride to be a bit harsher, perhaps that depends on the foam stiffness. The HAMB link has good description of foam firmness rating.
I am doing this because I am, to be honest, to Fat. I have not continued as I am new to that truck and I am trying out different padding in order to provide me a seat that fits me in it comfortable. For now, it is plywood and moving pad; plywood and sofa cushion, .... until I find a mythical sweet spot.
Btw, I did not want to chop the old spring frame up. I debated for a long time. It was hard to do.
As for truck seats, the air ride ones are sweet but probably may not give head room. Yrs back, being the rookie at the moving company, I got stuck with an old international that had a mechanical spring seat similar to air ride. Either of which are probable to big for application mentioned above... not really sure as I have never seen a coe in person(the international was a day cab conventional abt 1972 vintage and was small
