you want to try and prop it to get close to your max wot. for your motor that is 5500 rpm. by doing that you avoid lugging the engine. on an older motor i would definitely prop conservatively (err toward lower pitch) to avoid overworking a worn motor.
correct pitch depends on the prop. for most "standard" 3 blade ss prop like an oem model or mirage plus a 19" might work with a 225 on your hull, but a 17" is a more conservative choice. for some 3 blades like the enertia or any 4 blade prop, i think you could not go over 17 and might go lower to 16 or 15.
i run an old dinged 17 omc sst on a 1994 223 tournament with a slot transom and a 200 carbed evinrude which has a max 6000 rpm wot. top out at around 5300rpm. same hull. comparable engine with same gear ratio. your bracket might improve the wot a little and the slight hp advantage might be worth a little. i can't see fitting a prop bigger than a 17 on mine. after a fair bit of reading i purchased a 17" mirage plus and a 15" enertia this winter that i have not been able to try yet.
