Ok, the sourcebook idea sounds great, but you may want to look at the BITS website to see a variant on the "no stats" idea. They've got a free pdf download that lets you process tasks in a uniform manner across CT, MT, TNE, T4, and GT.
Maybe the answer is a meta-system description using basic skill descriptions. Equipment would be harder, although a basic paragraph description would work fairly well (it's how I "borrow" from other games, anyway). Weapons could be described in their basic lethality levels, so that they could be built in their home system by gearheads who care.
Just an idea,
Joe