The stock FI uses a different flow rate and it doesn't bother the pump, so I don't know why a pressure regulator would.
I'm not a pro on this, just a little experience. Keep in mind when I did it on my '88 it had no internal pump and I was going from a carbed 258 to the carbed 350.
That return line is probably for emissions purposes, which must not be a concern since you're going to a carbed engine. Which brings to mind the question, why going backwards with technology with the carb?