Classic/Antique Car Repair: what engine is this?, horsepower, passages

Question
I have a 1978 VW Super Beetle convertible, it had a different engine put in it. The number on the engine is: AD777381, I was wondering if you can tell me what year and type it is?

Thank you,
Roger

Answer
This was a replacement engine supplies by VW. This letter series was never according to my references installed at the factory in any car. Here are the specifications for your engine.
50 horsepower 1584 CC. Another note is that it has the enlarged oiling passages.
Brad