T2x, are you really going to speedmasters on the Wing?
V or I six?
Damn that is gonna FLY.... literally
As for the speedmasters, well it is more than just theory it has been done. I know of many STV style mod-vp boats that run 20" motors with speedmasters, some with 15" mids and then the STD 12" mid that they were designed for. The drive shaft can be extended to work on the long shaft motors. In all cases with the exception of the 12" mid an adapter plate is required to fit the speedmaster case.
Acceleration will suffer a lot!, two reasons. One being that the prop WILL not slip with no exhaust running over it and two, being that the props have no diameter ( 10 1/4 is the biggest from merc). Now here is another few problems, they are left hand rotation.... meaning you would have to rotate your 300X backwards..... and you will HAVE to religiously change the oil after EVERY run.
A few solutions are, have the gearcase built for RH rotation ( David Steckbauer can do this), and the run 5L inboard hydro props available from merc on them... up to 12" diameter.
The boat will be slightly faster, but in most cases the existing Sportmasters are run so high that here is really only skeg dragging in the water..... so there would be no change.
Bottom line, is they are going to be expensive, slow to accelerate, fragile, don't shift and only marginally faster........ how does that grab ya?