What affect would driving around with missing upper bellhousing bolts produce?

I bought a 1970 bus and later discovered that the previous owner(s) did not
install the engine with the upper bellhousing bolts in place.  They were
probably too lazy to put them in, and figured the cross-member will hold
the engine in place "good enough."

Not good enough!  There have been mechanical problems!  Chronic ones!

Question - What kind of damage would result from driving around for a long
time with the upper bellhousing bolts not installed?

Your comments are greatly appreciated.

Wolf

P.S.  I am deliberately not telling you what chronic problems have
developed in my Bus.  I am not testing your knowledge.