Yep, a 1960's Victa-made 125cc Mayfair 2, I'd agree. Could be either of Model 529 or 539, going by the engine number.
It's in exceptional nick for its age, too.
The carby is a Victa 3L, and a carby service manual download is on
THIS page - the Metal & G3 one. The 125cc/160cc Specs doco [Section 3] will also be useful for engine service info.
Note that only the top [numbered] section document links there are free downloads - the rest require a subscription.
The correct fuel/oil mix is 25:1. How does the compression feel? It may not need rings; they don't have much influence on smoke, in a 2-stroke.
