The manifold gasket will be the standard 1200 type while the rest of the engine will use the gasket set for the 1974 A13 engine. [it had the same 73mm bore as the A12]
If you ever decided that you needed pistons or rings for it then the same 1200 or A13 would be the source for these as well.

Everything that you would need to service or overhaul this engine would have been available in the US, you just need to know which models shared that component or part.