Sean I don't have the ISPL but I do have EMER WHEELED VEHICLES U 262/13 Trailer, Low Platform, RE, 2-Ton, 4-Wh, Rubery Owen, FV2508. Technical Description. Jun.1968
Is yours in the FV2500 series as well? There are 4 pages on the brakes plus a fold out diagram of the mechanical linkages.