K9, my GMC Maintence Manual lists the original auxiliary transmission as a Spicer model 5531-b. This is a three speed with a 2.36:1 under drive, direct, and .85:1 overdrive. Though, I believe a lot of junk yard scavenging went on in the past and a lot of trucks ended up with something other than what they would have had from the factory.
If you don't have a Maintance Manual, that would be a good thing to pick up. Mine has a green cover and is a number x-5209, it is specifically for models 450-470. And it is for a '52 year model with a revision date of 10-1952. I would imagine your 53 would be very similar. I also have a Master Parts Book, number x-152002. This shows you all the parts, and their number. Invaluable when going to the parts house, a lot of the numbers will cross over. These are a little more difficult to run across. Hope this helps.
You've never said if your truck had hydraulic, air over hydraulic or full air brakes. I was just curious because your truck is a road tractor. Mine is straight hydraulic.
Scott
