Yeah I don't know the tech details, never built a wheel myself, would like to but... I'd probably die from the imminent failure.
spacing would be 135, as everything mtb was 135 from the...lat 80 till pretty much recently. Old XT 737 was 8 speed, I am still running some of those parralex hubs as 9 speed, I think from memory had to change the freebody to run it, but it was so long ago, and I got my lbs to do it.
I've never actually thought about it, I 've got a pair of thse hubs I linked to to bulild up a wheel one day before non dics hubs dissappear, but no idea what is needed to run an old cassette...it says 8-9-10 speed, but my road wheels that are 10-11 speed came with a spacer to run 10 speed...