If it's all original, then it has a 10hp Tecumseh.
The Comet clutch is a 780 and the shaft is 1" so upgrading the engine is pretty easy.
It is either model 612-00 or 612-01...here is a link to download the manual with repair parts:
http://www.bmikarts.com/PDF/612_operatorsmanual_6120061201.pdf...
I think it's a good price and it looks in great condition.
I bought mine over 10 years ago and paid 1000.00.
I have put a Briggs Vanguard 20hp in it and the gearbox handles it fine. Running 23 and 25" Dirt devils.
I replaced the mechanical brakes with hydraulic street bike calipers and that...