Two things: First, I would not change springs ever unless I had a broken one. I've had several cars with over 300K on them and I prefer the look of a car with slightly saggy springs. It will have less air resistance hunkered down. If I had broken springs I'd prolly buy a used pair from a car with less miles.
Second: I'd not pull the motor if only changing the tranny. Its a lot simpler to just do the tranny. Yes, I've r and r one myself without a lift. These trannys are not all that heavy. You can use a floor jack if needed to assist....not that hard.

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.