A From the information contained in the
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Standard Lists it appears that the 6-ton Scammell will be plated for a gross train weight of 9.5 tons. This weight does not change significantly for any 6-ton Scammell models produced between 1951 and 1967.
Regarding your second question, there is no regulation which states that a vehicle cannot be used because it is not fitted with threeline air brakes. The stipulations are for 40 per cent retardation on the main braking system and 15 per cent retardation on a secondary system which may be the handbrake.
During CM's test of a Scammell threewheeler in June 1965, albeit a 3-ton Townsman model, mention was made of the problems of braking efficiency with this type of outfit, an overall efficiency of 40 per cent footbrake and 27 per cent handbrake being obtained with a Tapley meter. We suggest you contact your local Scammell agents before the vehicle goes in for test.
Regarding the conversion of your trailer braking systems, this should obviously only be done as a last resort. There can be cases where, quite probably, the whole axle assembly would have to be changed, as often original brake components are not available and also the hubs etc., will not match new equipment.