I can confirm it's not original, I would not like to say it is or is not 8 speed as I cannot measure mine to confirm it's the same length. I can conclude it's 8 speed from a bit of maths and the length you gave, that is all (of course 9 and 7 speed compatibale as well.)
My freehub, and the one shown on the photo have the threads for a Uniglide cassette, which yours does not. This just means that the freehub is likely to have been replaced at some point with a (likely) M910 or similar version as backwards compatability with Uniglide was dropped.
XTR started with 8 speed, moving to 9 with the M952 in 1999. 7 clicks in a shifter means 8 gears...