It's not the material that matters it's the pitch and diameter that keeps you in the max. rpm. Stainless doesn't flex as much as aluminum so the thrust is better.
Second step is buying a tach to see what rpm you are hitting; should be 5,500 or so @ full throttle; (this is on the high side which will help with weight) - setting the motor at the proper angle will help.
Hook up the tank line, tip the motor all the way up and pump the ball the old gas will be pushed out of the lines/carb. Tip back down and run normally.
The bearing carrier is probably corroded in place to remove it some guys soak the whole thing in ATF and penetrating oil for a while.
Heating the housing also helps.