Mike,
O859 1076 to 1127, which were Army reg no's 53BR76 to 54BR26. These were fitted with KL66 cranes, with a low mounted jib, the cab roof being lower in the centre to accomodate jib stowage. Crane built by K&L Steel Founders and Engineers Ltd. of Letchworth.They are described a general purpose cranes, so may not have been envisaged that they should go cross country.
The 6x6 AEC Coles cranes were described as a "Bridging" crane, and they were intended for rougher going.