Can't do it all at once: what's your reccomendation for order of suspension upgrades?

I think it depends too on what your intended purpose for the car is. Any racing involved? How much VS street driving?

I agree with the frame connectors. Far as I'm concerned, they should have been original equipment, even on slant six cars.

I would do those, then SS leaf springs (or whichever spring you choose) and go from there.