6 volt flywheels have 139 teeth (38-54/55 first). 12 volt flywheels have 169 teeth (55 second and up). The armature on six volt starters is larger in shaft diameter than twelve volt starters (5/8" dia. vs. 1/2" dia.).
Don't cheap-out on a starter for a rebuilt engine. Purchase the correct rebuilt starter so you don't have to worry about it later.
"Adding CFM to a truck will only help at engine speeds you don't want to use." "I found there was nothing to gain beyond 400 CFM."
