2bbl to 4bbl what kind of power increase

It will be modest but noticeable. IMO, before you do this intake swap, do yourself a nice favor. (Since you said "The hot rodder in me") Grab yourself a cam and swing it in.

Being that you have a all stock set up save the glass packs, IMO, I think that a Comp cam from would be a great idea. They have a small line (3 cam) of cams that are designed to work with stock exhaust manifolds.
Like this one; http://www.compcams.com/Cam_Specs/CamDetails.aspx?csid=635&sb=2
Or larger.