@Butch,
I can’t confirm which KTM model was used as the basis for the ALTA wheels and parts since they are Warp9 components, however I did some quick measuring with calipers in the garage.
It looks like my MXR, EXR, my spare EXR wheel, as well as my older KTM (2007) and newer KTM (2017) all have fixed mount, 260mm discs with the same thickness and bolt pattern; i.e. they appear to be dimensionally interchangeable.
The KTM OEM part number for the older dirt bikes (2007-2015) is
77309060000. See part #20 in this link:
2015 KTM 450 XC-W Front Wheel | KTM World
For newer bikes it is
79009060000. See part #20 in this link:
2017 KTM 350 XC-F Front Wheel | KTM World
The only difference I could see is a different wave pattern between the older and newer KTM rotors. I know the wheels are interchangeable by swapping spacers. I am pretty sure you could call the parts guys at KTM World (770-748-0771) and they could confirm whether the rotors are completely interchangeable. KTM World was also one of the first ALTA dealers, so they might even be able to confirm which rotors work on the ALTA wheels.
Note: Some of the KTM street legal dual sport bikes (e.g. 450 EXC Six Days) went to a floating rotor around 2017, however this would not apply to the ALTAs.
The OEM ALTA part number is
6801834-00 and the Warp9 part number stamped on the rotor is
A89-414. (see picture below) The rotor pattern of the Warp9 part is different from either KTM part, but the dimensions are the same.
Based on the pricing I have seen online, I suspect you could get the Warp9 part for about half of what the OEM KTM part would cost. My experience with Warp9 customer service has always been great.
I know this isn’t the simple answer you were chasing, but hopefully it helps.
-- ALTA OEM Rotor (EXR) --