The serial could put it at a '54, and the fact that it came with rim brakes leads me to guess it's a Jaguar, which if i'm correct, that'd make it a balloon-tire bike with a 3 speed, according to the '54 catalog.
Now, that serial is funny, b/c it could also be a 56, in which case it could be a Corvette or a Tiger, which would be middleweights with 3 speeds.
Surest way to tell if it's a middleweight or a balloon bike is to try and cram 4 fingers between the seat stays under the bridge. If they fit easy, it's a balloon, but if they don't, it's a middleweight. And once you figure that out, it'll pretty much let you know what year the bike was produced, too.
HTH
Rob
ps- tthe last pic looks pretty middleweight to me...