There are originally two counter sunk flat head screws that hold the drum on. If your truck does not have the screws, then the drum is probably just rusted in place. I had the same problem on my 49. I had to soak everything in penetrating oil and bang like hell(carefully) with an 8 lb hammer. It will eventually come off. By the way, if you do bend the backing plate, (like I did) it's not that big a deal to straighten it back out once you get the drum off.
