... I already have the heads from a 393w ... My question is, is it possible to fix the head and get it ported to get the volume I need, or would it be cheaper to buy new heads, and which ones?
That depends on what the 393W heads are. If they are stock heads - absolutely no. Ported stock heads cannot be made to flow anywhere near what the 427W needs to see it's potential. If the heads are something else, then tell us what they are.
... that popped the corner of the #4 hypereutectic piston off (everyone is telling me improper ring gap).
They are right. Urban legends persist for a very long time, and HE pistons got a bad name because engine shops ignored the warnings to use a larger cold ring gap so they would fit perfectly when hot. Of course, when the rings were heated, they grew more and end-butt. This seizes the ring in the bore and rips chunks off the top land of the piston. The failure is with the builder - not the piston design.
In-fact, HE pistons are both reinforced with greater hot strength, and use closer bore clearances for better power and efficiency. This is why the 5.0L HO and GT40 (Cobra) engines and most makes of factory turbo cars switched from forged to HE pistons as the technology matured. In most ways, they are simply as good or better, and less expensive to boot. Unfortunately, the urban legend continues, and HE pistons are still regarded by the general public as second-rate.