I'm working on a customer's car and it's got a Bus case. The owner said it's got Mahle p&c's, a "3/4 cam", and "oversize valves". He didn't know he had a Bus case, and not sure what other Bus components are in the engine.

I'm chasing some oil leaks and sorting things out a bit, and I found the TDC mark on the flywheel and impeller do not line up, there's 3-4 degrees difference between the two. The 009 distributor (to be replaced) is about 90* off from where a 914 should be, which is easy enough to resolve.

I have no experience with Bus engines, and wondered if the flywheel and impeller are indexed differently than a 914.

Any thoughts?

Everything should be the same across the type 4 engine line. Other than lower compression pistons the bus internals should be the same.

I think some fans have timing marks in different locations. They will fit and work fine but the marks make it hard to set the timing.

Bus fans are typically viewed from the front, not the top. And the have a timing gauge on the front of the fan shroud. Also make sure your not seeing some other degree mark, depending on the fan they could be all over.
Good Luck