there was discussion related to this subject some time ago, "should I 'update' a 950 engine with a 990 pump impeller and cover?'.
There was a supposed 'unofficial' view/response from a KTM engineer or something to that effect, that it was NOT recommended to perform this alteration to the cooling system on a 950. As I recall the reasoning was that the cooling passages on the 990 cylinder and head are different. When applying this change to the 950 (the change to the pump increases flow rate) there may be problems/issues related to coolant flow through the head.