I've been running SST HighFive (5 blade) props for the last 10 to 15 years and really like them for double-booted pull out for slalom. They are a bit pricy (~$450 new) and would suggest that you experiment with aluminim three blades to get a feel for what you need. The 75 HD I/O 351 CID 233 HP 2 Barrel came with a 21p three blade SST and I tried a 17p HighFive but the RPMs were a little high. Brought a 21p Highfive and the 75 gave up a bit of torque but worked fairly well. I have that same prop is on the 85 I/O 350 CID 260 HP 4 barrel and has great holeshot and top end speed. A 19 pitch would probably be a good choice for you in a highfive but see what the aluminum three blade does with the current motor. The throttle you are dealing with is a Mercrury and not a lot of flexibility. For the I/Os, I hav always run moris or telaflex throttles and they hide the cables up under the gunnel nicely. You can change out to the aforementioned but you will need to understand the travel or throw of the throttle and see if it works for you.