Also note that in 67 and 68 Chevelle AIM's M20 section, they show the backup light switch wiring clip being mounted to the other side of the bellhousing and that bolt is labeled:

"BOLT
PART OF ENG."

So the engineers obviously did not have any issue with allowing the car assembly plant workers to remove and reinstall a bellhousing bolt.

Makes sense - no gasket, no fluids to leak, and no risk of a vacuum leak. So not as risky a procedure as, for example, removing a couple intake bolts to add a smog bracket would have been (which I assume is why that bracket was already on the engine when it left the engine plant).

A little backup for Jeffs info.
This is from 68 Chevelle Assy book. The "part of engine" is also in other places.

Interesting to see the phosphate wiring bracket.