I don't have GMC books that go past the early 60's but I do have books on the engine. I didn't realize it was a tilt cab. However the 9000 series is the largest series GMC built. We had this same truck with a 478 V6 in it for a while, but it too was a gas guzzler. The same cab was offered with a 6V71 Diesel. The 637 would actually outrun the Diesel, but at the expense of using a lot of gas. The steel tilt cabs were designed for maneuverability in cities. They never found much favor on longer hauls. However, fire for fire equipment they worked well. I have no figures, but I would guess that fire equipment was probably the largest user of the 637. And fire equipment is quite often in mint condition because it was always garaged and well maintained.
