how much track time?
how many miles?
does it still shift properly?
As for telling the difference between a TKO and a stock trans (assuming you are refering to a T-5) here a a couple pics.
This is a TKO
This is a T-5
If for some reason you are comparing this to a T-45, there are no similarities there either. Basically, the panels on the top of the trans are the easiest way to distinguish between a Tremec TKO and a stock trans. Hope this helps.
TKO uses a 6 bolt shifter, well tremec in general uses a 6 bolt shifter. Do you have any idea if it is a new TKO the 500 or 600? Check the shifter out there is no taper on the shifter base for the newer TKOs. Depending on which one it is I would pay anywhere between 500-800.