I acquired a pair of these rotor housings in fantastic condition, they are obviously different from the 81-85 12a rotor housings-due to the routing of the exhuast ports with the Thermo-reactor tubing out below the exhaust port.

My question is do you block off these holes or exhuast will leak out through them by a later model exhuast gasket? Also, do you need to use the spark plugs meant for the 79-80 models- as the plug from a later one does not go as far into the hole as it does in a later model rotor housing. Is there any other differences with them?

 

if your running a header the flange will block the air injection holes if you use the correct gasket if not you can plug them with either aluminum rod or tap them with 3/8 NPT then use brass 3/8 pipe plugs and grind them flush. As for the plugs the later plugs will work fine in them or you have the ability to use the racing plugs without having to get the thinwall socket.