I'm working on some slight mods to make the '67-68 seat backrest cover work on my '64 seat frame, and it is fussy work, so I take my time and take frequent breaks to re-assess as I go.
In the mean time, I bolted the seat cushion into the truck. And, wow, that new foam and repaired side support spring made it like new. Or maybe even better than new. It is nice and firm, no squishiness at all. I sit much taller inside now, enough so that I had to readjust the mirrors.
I also note there is not a lot of thigh clearance with the rebuilt seat and original 17" steering wheel. So this just confirms that I'm going to want to replace it with a smaller (say, 15") wheel. I was thinking about this anyway, as you don't need a 17" wheel with power steering. Now it's pretty much a given.