I would say that the last digit might mean something other than the usual auto/manual trans deal.
However, that being said, I have not found any true comparison using last digit numbers. In other words it seems that carbs with the same numbers varied in relation to each other as far as ros/jets etc. Some are the same setup and some are not. I guess it is a big Rochestor mystery and so far, I have not really heard of anyone that has been able to explain it. Some have some theories but, so far, I have not heard of a 100% factual explination. My best guess is that it had to do with a convenience as far as production goes. Like maybe to differentiate which particular line or factory the parts went to.
As far as the rods go, who knows. Rebuilders and the like may have changed them. What is important is that you get something that works for you. If you have the "old style" of carb, which gmc and chevy used up until 1978 (I think), it will indee use the older style of rods. So, you can have an old stlye of carb even while the mod quads were available in the first few years. (75-76-77 and maybe 78 {??}).some of the rods were specific to the main airbleed setup in the later carbs (like the 53K with the 77 jet).
