Williams cabinets have always been such popular conversion choices that you really just have to look at everything to be sure.
Also a good portion of cabs on auction will either not list what the game originally was, or even list it wrong. There are some very experienced ops out there who actually can't tell from looking what game something used to be. Heck, Bob Roberts himself sent me a Dig Dug bezel when I ordered a Kangaroo one because he thought it was a Kangaroo one that he had. After I let him know about it he was like "Oops, sorry, I haven't played any of these games in 20 years". He got one from another op and sent me the correct one a couple weeks later.