No idea on the magazine. Have been a couple of shows on AHC and History channel on them.
Started out as 2 1/2 ton and went to 5 ton trucks. Even some M37 rigs early on. Usually double steel plate around the box, sandbags between. Armed with M60's, M2's, twin .50's, quad.50's, up to the electric 7.62 mini gun. Whatever they could beg, borrow, or midnight requisition.
Couple of replicas in existence built by guys that served on them.
Search "Eve of Destruction gun truck". Lot of information available.