The bellhousings are interchangeable... the flywheels are not. Clutches have to be matched to the flywheel and can be 9, 10, or 11 inch.
Depending on the year of the 270, it could have either a 4 or 6 bolt flywheel. If it is a 1956 270, it will have a 12 volt 6 bolt flywheel, however a 1954-1955 gmc 248 6 bolt flywheel will be a direct swap and will allow you to use a 6 volt starter. All 4 bolt flywheels are set up for 6 volts. You can run a 6 volt starter on 12 volts, but you can not run a 12 volt starter on 6 volts. Stomp starters can be found for either 6 or 12 volts, but they must match the flywheel ring gear. A 12 volt starter would be used on a flywheel with 168 teeth, and a 6 volt starter would be used on a flywheel with 139 teeth.
