For what you have and your budget, your best bet is a 383. The swirl port heads, while not ideal, can be made to perform.
If the block has flat tappet cam:
balanced 383 kit:
http://www.ebay.com/itm/311604465200...%3AMEBIDX%3AIT
or
https://www.summitracing.com/parts/e...make/chevrolet
XE256 cam and lifter kit:
https://www.summitracing.com/parts/c...make/chevrolet
if the block has roller cam provisions-
either of the 383 kits above-
plus cam
http://www.ebay.com/itm/COMP-Cams-Xt...dU~6IO&vxp=mtr
otherwise i would get a 350 new vortec crate motor from jegs. IMO its not worth it to buy used vortec heads then have them upgraded