The info I found on a search for Tokheim 558 is that it was used on 1988-89 Ford F800. Be careful, we don't do Fords here.
Some trucks had mechanical fuel pumps so it could difficult to find a truck with electrical pump in a junkyard.
Check with an auto parts store like NAPA. New harnesses are $$$.

The Spectra Premium Fuel Pump C6638EP may be a replacement for the 558.
Spectra is Canadian and makes good parts.
Maybe contact them to see if they have a generic wiring harness.

If the the bayonet connector part of the cable is in good condition, why not take it apart and make your own cable?

There are bayonet adapters that you can try but you would need to know the size of the socket (BA9, BA15 etc.).

"Adding CFM to a truck will only help at engine speeds you don't want to use."
"I found there was nothing to gain beyond 400 CFM."