I've been going down this rabbit hole since the thread was started. Its a fascinating topic.
Seems "midnight requisition" was the order of the day.
Some of them even used the hull from an M113 APC as the armored box on the back.
M60s', M2's, quad 50's and even M134 miniguns, quite the variety. Lots of room for "what if" builds if you're not into rivet counting.