I have an '89 RS with a 2.8L MPFI engine. I am planning on swapping in a crate 350 with carburated induction. Will my electric in-tank fuel pump supply enough gas to the carb? Too much? Will I need a pressure regulator?

 

You will need a pressure regulator. Get one that regulates pressure with a return port. They are more expensive than the dead-head ones, but your pump needs the return in order to have a good long life. I have seen someone use a dead-head regulator with a retun line adjusted with a needle valve - it's just simplier and more exact to use a return style reg.

The pump may or may not keep up with the engine, depending upon the engine you end up getting and the condition of the pump. In good condition, a stock pump can keep up with most streetable NA carbureted engines.

 

I'm planning on going with the Plain-Jane Goodwrench replacement 350 with a 650 cfm carb, not sure about the carb selection yet, but something fairly mild.

 

You could take the electric pump out and just get a mechanical pump.