Your KTM EXC was billed as an Enduro-Cross-Country model. At it's age now it's a trail bike. A really good trail bike.
A low mileage unit would make a helluva single-track bike or a weekend-warrior ride.
If memory serves, there was an issue with the ports matching and the X-dimension of the head.
There was a guy over at KTMtalk that worked miracles on these top ends I believe his handle was "claytm".
If it were me... I'd ride it once and evaluate its condition. If the bike was worth keeping, I'd figure out the top end (it may be perfect as is). Then I'd strip it to the frame LOOK CLOSELY at everything, I'd replace all the fluids put it back together and go ridin'!
Oh yeah, if it has many hours on it the carb will need to be replaced.
“I hate to break it to you but there is no big lie. There is no system. The universe is indifferent.”