Jim,
You talking about the small ammo box used on the M-23 door mounted M-60D's on a slick or the boxes used in gunships? Either way, they were not floor mounted. The only floor mounted ammo boxes were those used in the M-16 quad 60 and M21 minigun systems. The standard M-23 mount came with a ammo box affixed to the mount, but most units quickly replaced this with a 20mm ammo box or a wooden box of some sort. In the gunships mostly 20mm ammo boxes and wooden smoke grenade boxes were used. Here are a couple of pics. Let me know which system you are interested in and i think I can help you out. I'm guessing you are interested in slicks.
Ray
M-23 with ammo chute and standard ammo box attached:
M-23 with 20 mm ammo box:
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