Nice boat! FWIW I swapped out my standard heads with GT40 heads, made a noticeable increase in power. My posts about it areon here somewhere. I went from about 41-42 MPH to 45-46 MPH top speed, so I definitely increased the HP significantly. I believe Indmar also changed out the intake and cam when going to GT40 heads in the early 90's, so I'm sure I don't have the full HP of that motor, but close enough. Apparently the GT40p heads are even better, but I could not find them locally. I was lucky to find the GT40 heads in an Explorer at a junkyard where I could pull them myself.
Good luck with the rebuild.
1989 ProStar 190 with "Safe T Top", 351 Ford, GT 40 heads painted Ford Blue, Elec. Ign, 1:1, 720 hours, 4 blade prop, PP 6.5, removable platform brackets, custom color from factory, hot water shower, Boat Buddy & LED lights on trailer
2010 D3 Z7, 2 @ 32 off, 34 mph so far