I use this a frame when suspend towing with the pioneer ,the frame is only 4 ft long so if used as shown in the manual the casualty would be to close to the rear of the scammell and there would be no clearance for turning .
I position the roller against the front bumper/drawbar then strangle reevable chains around the bumper/drawbar and the roller of the A frame,these are then hooked onto the crane hook when lifted the roller is pulled tight but the A frame can still move up and down ,i have lifted GMC cckw AEC Matador Austin K6/K9 Ford D series etc and have never had any problems