Katman,
Please don't think I'm endorsing the setup because I have only bareshafted it and have just fletched the first one...
I shoot #61-63 recurves, typically pretty high performing (Carbon/foam etc), center cut or just past it shelf
28 draw, 29" bop, 350 spine, 620gr finished with 300 gr head, 45 Gr outsert, and the above mentioned 80 gr machine head 3" screw threaded into the backside of the outsert and glued in also. I believe the shaft is only 7.4 gpi. so why foc shoots up.
I think the balance point is 24"
Brad Isham is filling them with paracord, might give that a try also.
My 350 Widowmakers I add the same screw to and they land at 720 grains and fare they same identical weight and flight as my 340 FMJs .both at 28%-31% FOC...both are pretty hard to beat, again, I was intrigued by how well they bare shaft