That certainly sounds better than the original, and, it should be much better than the kit from JC.
What you describe is very similar to what my upholsterer re-did on all my Suburban seats. They are now relatively firm AND comfortable to sit on (relatively speaking).
Good luck - please post photos, and please give us a "ride report".
There will definitely be a ride report, but fair warning, it could be up to a year before this all gets together to go down the road. Keep getting roadblocks put up on other parts of the project. The plan has been to have it back on the road by it's 70th birthday, which would be in December, so we shall see. Not looking too hopeful unless I win the lottery and can quit working!!
