Yes, no, maybe...
Depends on how you define "restore correctly". As a trail bike, MXer, showroom condition, etc..?
Though a pretty simple bike, there are a few unique and/or obscure parts that may be hard to find (gastank, muffler, pipe, seat, fenders... though some repops are available, and less than correct substitutions can pretty easily be made).
Parts are as expensive as any other vintage Brit, but bike's value is on the low side, so you need to figure what makes sense for you... even a free bike could be too expensive. Peter at BSAunitsingles.com, who will probably chime in here, has most items you'd probably be looking for, and is well versed in this model.
What is the condition of the engine? Can't figure out what you're trying to say in your description. As a mechanic, it shouldn't present any great problems to you.
These are fun bikes, and depending on what you have to work with, and where you want to go with it, $500 may be a sweet deal... pictures would be a big help for getting opinions.