Join Date: Jan 2015
Location: Injun Territory, 'Merica!
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welcome! the route of obtaining and installing the thick Cometic head gaskets, not only expensive, but the big space is going to kill quench. A bad thing about cast rebuilder pistons, most juggled the pin height a little to lower static CR, and top of the pistons will set a little further in the hole, again killing quench. While the result has lowered static CR, much needed quench is gone.
Haven't examined a set of cast rebuilder pistons for 389 in ages. it would concern me on a set of cast pistons that good chance the deck thickness on the piston is too thin to machine a propper dish. The last cast set of rebuilder pistons I had in a running Pontiac was bought in a "local yokel shop" built '67 WT 400 which came in a package deal with my buying several '67 and '68 GTO projects. Traded that '67 WT off, as it didnt belong the either of the '67's, and a car builder wanted it for codes and dates. Long story short, the builder finished and sold the car, new owner has it in the 67 GTO, trys to run it on 91 octane, and within a year, detonation killed the top of several ring lands. I ended up being referred the new owner, and tore down and sent the shortblock out, had it built with new forged dished pistons and had the recip asm balanced. End use customer, very happy.
In your case, today, I would look at a set of affordable custom forged pistons from one source or another. A set of AutoTecs, properly dished, ought to run around $450 plus the cost of machining the dish...most likely another $150-175.