Heath,
You haven't got the message. Its Villiers powered. Only the major Villiers users like Francis Barnett and James ever did their own manuals, parts lists, etc. The minor players like Sun rarely did so. As their bikes were more of an assembly of bought in products Sun relied heavily on them to provide the info you are looking for.
You get the appropriate Villiers manual and parts list for your power unit, engine/gearbox/carb/ignition, etc. The MP data for the front forks is probably all you will find. The wheels are probably British Hub Co, the rear suspension units Armstrong and so on. Very little of your bike was actually made by Sun. About all Sun put out was the annual sales catalogue.
You have to remember your bike was made at a time when every young buck would start off maintaining his own pushbike as a lad then progress to a lightweight motorbike which was just a super sized push bike with engine and finally go full size. They learnt as they went along. Manuals as expected today just didn't exist. Thats why Haynes Publications started, they filled the gap. Unfortunately there aren't enough Sun Challengers around for Haynes to do a workshop manual on them.
Don't worry it isn't that hard. You'll be fine.
Cheers,
