Wow, thank's guys for your messages, the tickover problem may just be poor adjustment of throttle linkage or something else, won't know till we get round to it, you've pointed us in the right direction though.
Think we have the compressor working now, the valves were a little bunged up, but the bores were spot on, pulled the aux gearbox apart and its in good condition.
Two problems have emerged at present, the rear pinion has suffered a little damage and will need to be replaced, does anyone know if these are still available and are they common to other AEC vehicles?. The next is the chassis has cracked both sides just behind the cab, it has been repaired at sometime but they have only welded the outer surfaces and poorly at that, must have been done out in the field.
Good news, all the brake cylinders work and hold air, we were a little unsure if they would.
Will post a few more pics when time allows and things get done, cheers for now, Gareth.