I'm using a Scat Powerforce+ D90006 SFI harmonic damper. This damper has both 3- and 4-bolt accessory bolt patterns, has a removable counterweight if your engine is internally balanced, and is the exact same part sold directly by others as the Powerforce+ D90006 damper. It used to be available at a substantial discount when purchased through Scat but I don't know what current pricing is.
I'm using this damper on my 383 stroker, the interim 351C from my Mach 1, and another PCNC member has it on his 600 hp 393 stroker.
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