One of the original
Bob's Big Boys is in Burbank, probably 40 miles away, and that would be one expensive taxi ride. If you're intent on it you could do Metrolink/Red Line Subway to the Universal City stop, and that's a couple of miles from Bob's.
However, if you want a 40's drive-in experience complete with car hops on roller skates you could go to the recently opened Ruby's Diner on Lincoln near West Street in downtown Anaheim. You'd be eating in the diner of course unless you want to treat the taxi driver.