So I'm guessing that the Pro Max is the single air opening fuel injected rig without the air pump and fancy ECU but with a nylon oil pump drive. When I saw the model year, I was envisioning three two barrel carbs. Sigh.
The 225 Pro Max is a laser injection 2.5 liter steel bore Mercury. Pretty close to the 200 fishing motor but with a 260 exhaust divider, different coil holders and the 7 petal fiber reeds and slightly higher compression (37 CC heads ) and thinner rings on the earlier versions. Same fuel management system as the 2.5 fishing motor 150/175/200's except for the 7 petal intake. It does use a higher rev limiter ECM and generally come with the heavy duty lowers. The late blocks like mine use the rod slot ported sleeves like the 240 sport jet but Pro max uses head gaskets. Most dyno tests on the 225 ProMax's show closer to 250 HP at the prop in stock form.
This is mine with a spacer to unshroud the outer reeds and a Brucatto ACU.