My point is that you are going to spend way too much time and effort for very little realized gain. You would be far better off on sourcing a suspension seat post and keeping your intact saddle. Labor isn't free even if you do it yourself, it still is a tangible asset.

Suspension seat posts are adjustable so you can alter the preload as you wish. Doing so on a hacked up saddle won't nearly be as elegant.

You sound exactly like the guy who modified the Ford intake to work on a Caddy engine. You are trying to spend a large amount of time on solving a problem that has already been solved. I bet you could find a cheap suspension seatpost somewhere like your local bike coop.

Personally, I would just soften up the preload on the adjustable seat post and then put a normal non-spring saddle on it and ride. Is there a reason why you are so against a suspension seat post?

Also a Harley's hardtail suspension seat isn't feasible on a bike, apples and oranges.