The blower on the 2 cycle Detroit was needed to fill the cylinders since it was a 2 stroke. The air boxes need to be pressurized to push fresh air into the cylinder when the piston uncovered the liner ports and to aid in pushing the exhaust out the exhaust ports. Without having my engine manual in front of me I want to say it is something like 4 PSI above ATM. The blower is gear driven off of the gear drive system on the front of the motor.
Being a 2 stroke the 2-71 has the same displacement as a 450 (284 vs 281 CID) since it is firing on every stroke rather than every other. IE they are moving roughly the same amount of air in the same amount of time.
Getting more power out of these motors isn't difficult. Easiest way is by simply going to larger injectors. The 2055 came with 60 cm (cubic millimeter) injectors. My motor has 70's. The real issue is the bodies. The fuel inlet / outlet are not staggered so it takes some doing to get large injectors built to your liking. Interstate McBee can get you the old style assemblies and that is where mine came from. Actually I have a whole basket of old style injectors that are frozen, etc in case I ever want to have them rebuilt into something "meatier"
RPM's are increased pretty simply by the turn of a screw or two on the governor. The biggest draw back to making huge power with the 2-71 is the 2V cylinder head (There was never a 4V head made) and the low block configuration (all 2-71 engines are low block - use a full head gasket) which precludes you from using large port, high compression N series components.