We had quite a few Sun VTS machines out here in the war years, either branded as "Sun", or sometimes painted up in the livery of a local manufacturer. I did some work on the attached engine for a friend a while back: it comes from a bike that was branded "Bullock" (Adelaide cycle manufacturer), which was in reality just a re-badged Sun VTS. These bikes were distibuted in Adelaide by local firm James Hill & Sons, Ltd. At the time we couldn't locate an appropriate oversize piston (deflector type), so the compression is poor. If your engine happens to have good compression, and you'd like to part with it, let me know and I will pass details on to my friend.
Leon