Hey Chris -
Thats a very nice A3MP! Amazing all of these early 'Tags popping up right now. The only difference that I can see is the A3MP used a specific water valve vs. the AMP and A2MP that, per the parts lists, used one of 3 different types. The front name plate is the same on the A2MP/A3MP. Hopefully someone else may have more info on the differences.
Nevertheless, you have an amazing machine there! I wondered why you were looking for boot seal earlier... =)
Ben