We are trying to identify the successor companies to the Jack Hoffman
Insurance Agency.  The company was an insurance broker based in
Philadelphia between 1948 and 1968.

Does there have to be a successor to an insurance agency/broker?
They can be acting for one insurance company or be independent,
selling insurance for different companies, and the pertinent documents
would be with the insurance company either way.  If Jack Hoffman
retired in 1968, he may have turned over his files to a successor, but
I doubt that inactive files that are over 30 years old have to be kept
 - remembering that actual documents for an insurance policy would be
with the insurer.
If you want to trace something having to do with a policy, perhaps it
would be helpful if you could explain that.
Myoarin