Power Unit Serial Numbering? I think I got an early one

[Super A]

Yesterday while completing the valve lapping on my 52R combine engine, I happened to take time to actually read the tag on it. The prefix indicates a combine ("harvester-thresher") and is 52HT, since it's a 52R combine. THe really interesting thing is the actual power unit number is 580. Did IH number its power units the same as their tractors--beginning at 501?

I didn't write down the serial number on the engine block, I think the prefix starts out ICUBM or something like that, I know from past research it indicates that engine was meant for power unit service. The casting codes are '49. The actual combine serial number is not readable, (for some reason, IH used decals--an individual decal for each numeral--to number the 42R and 52R combines.) However, IH began offering the Cub engine instead of the Continental engine (the combines came standard with PTO drive from the tractor) sometime in 1949 according to the parts book. SO-oooo, I wonder if I don't have an early Cub-equipped combine???

Progress update: Pulled the manifold to clean out the passages, Got the valves all done, head all torqued down, got to go out this morning and pick up maifold gaskets. I should be ready to try to start it soon....

Al