Fast Scarab, yes i do but I dont believe it has one

350 mag WOT engine rpm per mercruiser is 4400-4800. You're in the ballpark with diameter. Odds are your money would go further talking to Greg at Cutting Edge Propellers about getting your existing prop woked/labbed. FWIW, a laser 2 21p on my 94 22 Scarab with a 350mag/alpha setup has pulled a best of 60.9 with two people in the boat, half a tank of fuel, and 75* air temps.