If you want to replace the heads go with the Vortec heads & a new GM Vortec / TBI conversion manifold.
Our 88 K5 Blazer has a Comp Cam for a TPI engine that runs well w/ no computer mods.
Put some flat top pistons in there, a heated O2 sensor & a set of headers as well & it will run pretty good.
Here's some more info
http://tbichips.com/?page_id=73