Al is correct for everything except the ME rating. All differences training is just a log book endorsement. I have some funky little stickers that I put in the students log book to sign off the various differences, in FAA land it is just a signature and comment in the logbook but same end result.
The ME training will carry over but you are required to sit a flight test to get it added to a UK/JAA licence as it is a Class Rating not differences training.
Al, you also need to re read the question, the poster has a JAA licence with a based on FAA licence and wants to get some differences training and want's to know if it can be applied to his JAA licence.