[tubman]

How does that engine breathe? I see it has an early intake manifold with no provision for a road draft tube. It does have the early style fuel pump stand where the air can get into the engine, but how does it get out? Unless provisions have been made for the air to get out some way (such as a PCV valve), it can cause problems. The air flow through the later (8BA,8CM) engines is opposite that of the earlier engines, so swapping intakes late for early is not a simple bolt on exercise.

BTW, I would consider changing out that intake manifold in any event. It's a textbook example of poor fuel distribution, especially if run with a straight linkage.