Changing from two handles to one lever?
#1

My fiberglass tub with surround has to be replaced. It has two knobs and a shower thingy in the middle. How much work would it be to change that to a single lever type modern faucet? I'm tearing it all out to the bare walls so I figured I might as well think about this. There seems to be more choices in single-handled faucets.
#2

Since you are replacing the surround, changing over to a single handle valve is no big thing. Just a matter of getting the pipes reoriented to match up with the new valve. A 2 or 3 handle valve has the hot and cold coming in on 8" centers, and most single handle valve have the pipes coming in from the sides. A couple of elbows and a couple of unions should be all you need.