Nothing I have found fits w a 15 5/8 prop. Looks like it could be costing me w those big holes in the upper unit exposed. It looks like a recessed part could be made to fit in the holes and I was wondering if anyone CNC'ed one up. Thanks in advance

Is there even a perfomance loss without having a block off deal?

if you are talking about the holes in the cavitation plate and you can get on plane without any issues then it won't effect the performance in terms of speed, if you are having any cavitation issues planing, turning ect then you should block them off.

Thank you ! I was worried about loosing top end numbers