I recently picked up a type 1 engine that was apparently rebuilt to go in a plane. It has three extra threaded holes in the case around the pulley. Could they be for a bypass cooler, and can I plug them
a pic will help us help you mate.
Probaley a universal case that can also be used in a type 3 as they mount the engine hanging frame from those three holes as a type 3 doesn't have chassis horns as such
Here is a photo. The two bigger holes are on the left and right, the smaller one is down the bottom
Yep, 3 point mount case, used by VW for the later Kombi and Type 3 engine support bars
do I need to plug them, and if so what is the best method
should be fine as they are only mounting holes for a brace.
Yep, as the others say they are for a rear engine mount bar. I've got one of those crankcases in my bug at the moment and I didn't put anything in the holes. They're blind holes in the casting so they can't leak anything.