Differences between D7 3T and 17A

I have a neighbor that might part with his 3T. Is there anything to be particularly watchful for on the 3T and what are the major differences between the 3T and the 17A? Thanks
He didn't have the serial number but thought it was about a 1950.

Main difference is the engines...D7 3T uses the D8800, 17A uses the D339. both 5-3/4 x 8 bore and stroke. The 17A's were all oil clutch, the 3T might be dry depending on serial number. Both good tractors.
The 17A's came with either even fire or odd fire pony motors (don't know why??)

Thanks OM!! 😊

All the early tractors that were even firing had the mag up on top of the front cover of the starting engine & the odd firing had the mag. down on the front cover of the starting engine that I recall.Without parts books I can,t say when the change came or if the 17As had the odd firing but I know the higher SN tractors were the odd firing.I have a D8 14A & 15A operators manual & it has the even firing engines in them.Another difference in the odd firing & even were the crank rod throws on an even firing were on the same side of the crank where the odd firing the throws were 180 degrees apart or opposite each other.