I THINK that the Mk I relates to the version of Tracked Towing (TT) configuration rather than the version of the Loyd that it was based on. You will find very little about the 'Anti-Tank Mk 1' but loads about the Loyd TT for 2 Pdr / 6 Pdr, in my view they are the same machine, just a change in nomenclature. I'll have a look tonight at the manuals.
PS. I've got all of Pauls restoration photos as he stripped down the Loyd, its all original to the vehicle, you are very lucky.
Edit: I was wrong.... just found ref in the November 1944 parts book to the MK I TT, it says the first 1630 machines had the old style track adjusters, which means Bendix brakes were used. I would imagine that means the early TT contract started out as Mk I and then changed to Mk II but were never officially re-classified during the production run at M.B.Wild.