looks like a twenty pound co2 bottle (get filled at a welding shop) american type d sankey coupler, which will be good for most american commercial kegs (get em anywhere they sell kegs), looks like theres a hump on the bottom floor of the kegerator, but is that a shelf, if so you could fit 1/2 barrel keg, if no shelf than 1/4's or 1/6's.... dificult to tell without measurments.
Also if I were you, I'd replace the beer line with new line, its cheap, and you probably don't know what the PO's cleaning regime was like. Also tear apart the faucet, and scrub it, if it's really skanky, replace it. That way your sure you get nice clean, delicous beer.
Manasquan River Brewing LLCManasquanRiverBrewingllc@outlook.com
"Custom Hand Crafted Fine Brewing Implements, Mash Paddles & Wood Working For Brewers by a Brewer. Serving both Pro Brewers and Home Brewing Customers"
Available thru the Fine Folks at MoreBeer! Inc.
Also available thru select Local Home Brew Stores World Wide.