$950 is a pretty decent deal really.
As long as the supports and tunnel are straight (no accidents), the motor would not cost much to rebuild if there really is anything wrong with it.
I'd go for it.
Just rebuilt a 670 HO and spent just under $400. Tough motor to find parts for (HO = High Output = Higher Compression)
2015 Skidoo Renegade BC 600 Etec
1999 Skidoo Summit X 670 HO (Son's)
1996 Skidoo Touring E 380F (sister's)
1995 Skidoo Summit 583 LQ
1985 Skidoo Tundra 250F
1999 Arctic Cat Jag 340F
1999 Arctic Cat Z 370F (son's) - needs track
1990 Arctic Cat Jag 340F
1982 Arctic Cat Panther 440F