I bought a bunch at the Long Lane Tractor auction for just a few bucks. I have three with no wheel weight holes and riveted construction, one with no wheel weight hole and welded construction, and a whole bunch of ones with round wheel weight holes and welded construction.

Can anyone document when Ford changed from one type to another?

According to smiths website early 8n 19" was standard. 16" optional intend for loaders. The 16" ones with no wheel weight holes were used until 1950. With wheel weight holes 1951 and up.
I have a 1950 front dist. that has the ones with the wheel weight holes but I don't know if they were changed. My 1951 has the same wheels with the holes.
Kirk

Kirk:

My 51 side mount has the 16" with holes. No evidence that it ever had a loader on it. The front end and steering is good and snug, as is the rest of the tractor which makes me believe that a lot of people that didn't use a loader opted for the 16" wheels. 600x16 was a common auto wheel size at that point in time which gave the owner a wider choice of tire types to choose from.

BeeMO