Well I ended up buying it. Man, that was a long 30 mile drive home when I could only muster 1500-1600 rpm out of it. I should have looked at the tractor a little more cuz it has a throttle adjustment screw under the dash that gave me a little more rpm, but I found that out after the trip home. Oh well. 

Well, after doing a little research, I think I might have a Frankenstein tractor. The model number is 185-2204. The serial number is 153012-427. This puts this tractor as the second to last 1850 built in 1964. That's all fine and well, but there's a few other items that don't add up to me. The engine casting numbers on the block are 155720A, 221120, and 6213. I'll get the stamped number next time I'm near the tractor. I was told the block was cast in June of 1963 and that it is an 1800C block. Make any sense to anyone? Also, the tractor has a generator and I was told that no 1850's came with generators. However, the carb in a USX-37, and those only came on 1850's.

What in the world do I have here?! I don't mind that the tractor may be pieced together, but I would like to know what I have to start with. Thanks for the help.

Also, where can I buy a build sheet for this tractor?