Buggingout,
With regards to the medical; what i wrote in my previous post, is what is written down in the current 14CFR. If an FAA employee told you otherwise, make sure you get it in writing. You are always responsible for your actions at all times!
With regards to the aircraft, i feel we might be talking apples and pears here. Looking at your location (UK) and some of your previous posts, i assume you have a JAA license (correct me if i am wrong, if you don't, disregard the following)
In the JAA system, you get a category and class rating on your license (ie Single Engine Piston aircraft) This allows you to fly allmost all single engine piston aircraft. Theoretically you could buy any SEP plane, read the manual and fly it. You don't legally need any endorsements, or ratings to fly a different SEP plane. Checkouts, school/club/insurance policies have nothing to do with what you theoretically are allowed to fly. So you will also be allowed to fly any plane in the FAA system.
In other countries, the local regulations require you to have specific (flight)training before you can fly a different make/model. (I believe South-Africa is one of them, someone correct me if i am wrong) So if your FAA certificate is based on such a license, you can only fly the ones you have had your training/endorsements/authorizations for.
Same as for above, if someone told you otherwise, make sure you get it in writing, it's your butt and license on the line!!!