What's a good starter suspension system that can be upgraded later?

-Hotchkis or Hellwig front sway bar and rear adjustable sway bar.
-About .97 to 1.03" torsion bars
-moog offset pn. 7103 upper control arm bushings installed for more caster
-rubber LCA bushings
-poly strut bushing with rear bushing cut 3/16" off and steel tube the same amount.
-Bilstein RCD shocks

Reinforcing the K-member would be great if it's out of the car and it fits your budget. It's a core piece that's a lot of work to do later. But it's not as "bang for your buck" and "feel it in the seat of your pants" as the items above.

Use your current rear leaf springs if they are V-8 units. They are probably sagging enough where you will not need lowering blocks and front lowering perch. Hotchkis special handling leafs are great if there is room in your budget for them. But they will lower the rear a lot. OK if you want the front is lowered a lot to match.