Very few L-engine parts can be used on a 1200 without modification. The carb is larger, different bolting holes, the manifolds are different, etc. The engine does not "bolt in", but is small enough to fit with some modification. The transmissions are very different.

The one thing that might fit without modification is the alternator. The 620 alternator (50 amp vs. the stock 1200 35 amp) bolts right in. The 720 alternator might also.