I was going to do the alternator upgrade with the Motorsport alternator upgrade plug but they said won't work on '73 becaused of electic fuel pump. I know some disconnect the electric pump but is there a way to still use it & upgrade. Does it require rewire of fuel pump? Any alternatives? Need to do this upgrade to proceed with the other standard upgrades such as radiator w/fans, updated lighting, & etc. Help deeply appreciated.

GM 1-wire. Do it. Been discussed many times.

The 1 wire alternator is the way to go. I wire from the alt to the battery is all that is needed. Here is a bolt in kit:

https://zcardepot.com/electrical/bat...80z-70-78.html

That still does not address the OP's issue.