Hi Mike,
Here is what George e-mailed me when I did mine in 2009:
Hi Mark; Probably the best source is EGGE Machine. They are cast pistons, in 10:1 comp. But when assembeling the engine, the rotating mass has to be rebalanced to plus or minus 2 grams, just as the factory did on these 300 engines. All aftermarket pistons are heavier than factory. Every engine I rebuild is rebalanced. Approx. balance cost is between $185. to $350. but well worth it for a good running engine to duplicate factory. There have been other suppliers, BADGER, FEDERAL MOGUL, but I am told they are no longer manufactured.
Also, when rebuilding, do not forget to have the shop install hardened exhaust seats and the "dampened" valve springs and "premium" valve seals for long life.
If any other questions, you can give me a call, 517-849-2783.
George
Mark Knutsen
I'm looking for a set of 413 pistons, preferably .030 or .040 over. I see a lot of truck 413 pistons available but not flat top and the compression is too low. I prefer cast over forged or hyperutectic. Please pm me.