it's the 873 style cabinet, but that game is a5 line machine
it's a 1090 type machine - 3 coin multiplier - but the 1090 had wide reels.
it's probably a 873 converted to a 1090. Some conversions are very good ... wire colors matching schematics, etc. ... others not so good.
there should be codes stamped into the slotted reel index discs, an M-645-xxx number on the payout counter disc, and if you are lucky some writing/info on the reel wiper contact plates that will help.
if you can email highest possible resolutions pictures of the entire front of the game and the reels, along with the insides to slotpics@cdyn.com, I'll see if I can match things up.
you can find freely downloadable paperwork for various models at
https://bingo.cdyn.com/slots/