how much $$$ you looking to spend in the long run is the question?
if you are done with bolt ons and looking at some big boy mods then i'd start at the drivetrain. i've got a yank ptb3200 stall converter and i'd highly recommend it. depending on what you are looking for you may want to go with a lower or higher stall. for example down the road if you are looking at a cam that will do better on the top end then you'll want a higher stall.
of course the reason i say start at the drivetrain is because you'll want to do some trans mods regardless. shift kit, servos, clutch pack, 2-4 band, sunshell, sprag; its about $1k worth of parts plus labor on top of that but if you're looking at making your brick haul ass then you'll have to do it regardless
After that i'd go cam ($400 for a cam, $500 for valvtrain; springs lifters pushrods etc.. plus labor) again what cam grind to go with depends on what you are going for
if you're going to get some fancy heads then do that along with the cam. an experienced builder will be able to lead you in the right direction. alvin at pcm4less has put down some nice power with some of his combos.