[Gaz64]

I've seen your thread about show your valve covers, and you've probably seen the thread link for another guy with the same issue.

The trouble is the early IDFs had a different pump actuating lever, roller follower like IDA, and would have had no clearance issues.
The linkage became like Dellorto DHLA at some point, probably when they became non-Italian.
The manifold was probably designed for early carbs.

A bit of a problem to come up with a good remedy. A brazed in welch plug might work if you have rocker clearance. You would have to cut the lid off a rocker cover for experimentation.