Re: what is this motor?
I agree that the motor could be a TD-20 or TD-15. The forward facing "horns" on the motor tipped me off to possible early 50s vintage, but I didn't realize that the 40's motors had that feature also.
I just did a little surfing and I think Steelspike is on target - the earlier 5hp models look essentially identical to the 50s series motors. I also ran across something that suggested that there was a "TS-15" motor made in '41, in addition to the TD-15. I don't know what the difference between the two was.
One thing that I am pretty sure of, is that your motor is not an early 50's 3hp. From everything that I have seen, that motor has a different midsection and gearcase. Its basically the same "weedless" gearcase that was used on the 3hp and 4hp motors from the 50's through the 60's.
Unless the items in the sale have major problems, I think I would be inclined to go for it. I might also be inclined to pay a couple of hundred bucks for the motor alone, just for the "cool" factor! If it runs or can be made to run, that's just lagniappe!
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