Dating a Farmall Regular

[CWAMuseum]

The museum has 3 Farmall Regular tractors. None of them have a plate on the toolbox - only those lonely little rivets. I'm confused about the difference between the frame rail number and the QC number on the engine block. I think the frame rail number is the "real" serial number that would date the tractor, whereas the QC number is for the engine. I have the serial number list for the Regular. Am I correct that the frame rail number is what would be looked up in the list?

I can read the QC number on the engine block on one of them and with a little work, might be able to reveal it on a second. The third is painted over and will take a lot of effort to make it readable. The frame rail number is clear on one of them, and with a little more scrubbing should be visible on the second, and the first two digits of that number is clear on the third as it has something bolted over the top of the rest. However, with the first two digits, I can get it in the right year.

I don't want to waste time cleaning up numbers I don't need in order to date these. Please advise.
Thanks in advance.

 

[formerly ny bill]

I have Oscar Will and Todd Markle's "Collector's Originality Guide for Farmall and F-Series". Also 3 1/2 Regulars, but I am by no means an authority.
From the Guide: the 38xxx serial number was built in Sept 1928.
43784 was built in Oct 1928
QC 13270 was built Aug 1927
Guide says that "according to IH documents, no attempt was made to match chassis and engine serial numbers, although many have been found to match".
QC was built at the Tractor Works in Chicago, alongside Mc-D 10-20s. The others were apparently built at the Farmall Works in Rock Island, Illinois.

 

[mschwartz]

I think that the frame number is the one that would have matched the original tag. Engine numbers got larger than frame numbers later in production I think because the engines were also used as power plants on combines and other equipment. Frames are also less likely to have been switched, looked at lots of early tractors that either froze or threw a rod and had the block replaced. Good luck, Mike