Seb, Pacman :
The Sternpowr leg can be close coupled directly on to an adapted borg warner box. (to close couple a gearbox the driveshaft bearing housing has to be removed from the leg). Also any box / engine combination can be coupled as the drive has a standard drive shaft flange. A universal shaft can be bought or made which is telescopic and would therefore fit different combinations of power units.
However all this costs time and money. With the costs involved, if i were considering repowering I would consider a different hull to start off with, probably a slightly lighter 7 metre hull.
The P22s are great, but the are ideally suited to a 4 cylinder engine and the sternpower leg. In my ming there is no point altering that set up for a few more knots when it would be easier to start again..
Also they are a heavy boat, and puting in a 250 hp or even 300 hp engine will make it even heavier for its length......