(even if you have an IMC as the FAA don't recognise that rating
True, they don't recognise it, BUT IMHO having an IMC rating lifts the restriction of "in sight of the surface" from the ANO. Many people disagree with me, but many I've spoken too also agree. Its a grey area basically, but I believe that if ramp checked in the US you'd be legal ( a) becasue the "normal" FAA PPL is allowed "on-top" and b) due to the fact that the IMC rating allows you "on-top" in the UK).
You do NOT need a FAA medical as pointed out, but you can have one if you wish. I normally get my JAA class 2 renewed by a dual FAA/JAA AME who's happy to issue my class 2 FAA with no extra examination, and only a £10 fee......
One other note, don't forget to complete the "Verification of authenticity" process before you go.
EA