Hi Rob,
I think we are on the same wavelength, Mk1 and 2 with crab steering option and Mk3 without. Regarding the transmission, yes Allison. I think the Clark box I changed was on a Hydra Husky crane which sheared its drive in the box.
I remember having to overhaul two Muir Hills that had just returned from an exercise in Gambia, they had not been cleaned and everything was covered in bright red African soil. One required a replacement hydraulic pump, no easy task to get to it over the engine and down under the boom. Once you were in there it was difficult to get out again!
Simon,
Regarding rear ballast they usually operated with either the Massey back-acter or a Boughton,winch and spade, then you had a good counterbalance for working the front end.