I don't have books on Chev but I would suppose what you have is an Eaton 1350 2 speed which were used in trucks of about 2 ton. They were available in the ratios I mentioned earlier. Heavier rear ends were the 16000 series. These were 3 ton which Chev did not build until the Task Force series. I'm not sure that Chev offered all the ratios that GMC did. However, a complete rear end from a GMC would fit a Chev. If you have everything to shift the auxiliary, you will be fine. It is often that people buy an auxiliary only with no linkage and then have problems finding linkage. If you have got all the parts, it would probably be the simplest way to gain a little more speed. The only modifications would be the drive shafts, but I'm sure there is a driveline shop near you.
