273 upgrade to 4bbl?

One factor that you’re not mentioning is what is the rear gear ratio? If your stuck with a highway gear, no 4bbl is going to give you a lot of power except when your getting up to speed. It will improve but not what you may be looking for. I would invest in the 8-3/4 first with a better gear for the street then go for the 4bbl.
JMHO
Syleng1