Old ABC STs are known for being high compression, low nitro engines. So if you want to optimize the running conditions, get a stack of head shims and lower the compression to the point where you can run 30% fuel without blowing plugs alot. Running the engine on the bench with an 8x6 prop and at a rich scream for a minute, then cool down and repeat a few times will condition the engine for "prime time" On the MAGNUM I would think an APC 8x8 would be a good place to begin. Up grading bearings is a good idea, PERFORMANCE SPECIALTIES might stock some good bearings, it's the rear bearing that can fall apart. You can also just buy some balls and load your own, "full compliment bearing " that will never fail and has no drag that is caused by the retainer, because you remove the retainer and run balls and races only..