Hello Greg!
These Mills Bell-O-Matic open front style slot machines when used in a casino environment would normally sit in a bank of slot machines which would have been on a long cabinet with a coin payout tray incorporated into the cabinet that would sit in front of the slot machine for the payout from the payout slides to be dispersed on a winning combination and as well would have had a door in the front of the cabinet towards the bottom of the cabinet to access the bucket below the slot machine to catch the overflow coins or the casinos "take" which would have usually been collected once a week usually on a Wednesday night graveyard shift to have the least interference with casino customers, this was called "doing the drop" in reference to collecting the coins that "dropped" out of the bottom of the slot machines!
You can either try to find a stand like the one pictured here below that is made for that style slot machine, which are not easy to find as no one I know of now is mass producing or you can build yourself a small base and/or use an existing cabinet and insert a tray into the area below and to the front of the slot machine for the payout coins!
These stainless steel trays are readily available from a restaurant supply house and come in different sizes and are used as serving trays in a buffet steam table and are relatively inexpensive and have a nice sound when the coins hit the tray after a payout!
They have a lip on them that will allow them to sit nicely in a cutout that can be made with a jigsaw in the appropriate cutout size!
Bona Fortuna!
MONTI