Blake,
there were two series of radios for the 47 to 53 Chev/Gmc pickup. The 47 to 50 model had a back with a joint that was on a slant on the side of the radio. The 51 to 53 model had the regular rectangular shallow back. Both models look exactly the same when installed.
The speaker was a 5x7 that was mounted inside the radio. The modern 5x7s fits quite well into the 47 to 50 model but not the 51 to 53 model. These modern speakers are the same as sold by Walmart.
The radios are a very popular item right now and in fact in the summer, unrestored examples were going for $350. Some big vendors like Jim Carter offer them for sale, restored. Also there is a thread in this forum that points out a brand new model, not a conversion, with modern electronics. These units look almost identical when installed.
You can see examples by doing a search for "47 truck radio" on Ebay.
