Seagoon, I have a number of good books on US armor ,but they are in storage:( and I no means to get at them quickly. So I am going from memory...
I beleave the Buffalow's 20mm was a purly British mod, I am not certain if it could be used for AA defense, although I suspect so.
I beleave US LVT's had the side 30 cal, but as I said I am not 100% certain.