I've been following this thread with interest, and would add the current class specifications that I know of in certain European national championships. Naturally there are also regulations on tyre width, suspension, tyre warmers or lack of, etc. etc.
In France, the VMA run a 650cc Vintage class, which is for 351cc to 650cc European bikes, up to end of 1970 for 4 strokes and 1968 for two strokes, with drum brakes. This was increased from 500cc to allow 650 twins. Next year will see Japanese singles such as the Yam XT/SR 500 and the Honda XLS 500 included. This should not only increase the grid numbers by lowering bike costs, but make for interesting racing. How will the Manxs andf G50s do ?
In Spain, the Class C is for 2 strokes up to 350cc and 4 strokes up to 500cc, all single cylinder with drum brakes. This allows the TSS and AJR Bultacos to rule, witness the speed trap figures. But they normally have good numbers on the grid.
In Portugal, the Class C1 is for bikes up to the end of 1975, single cylinder 2 strokes to 350cc, twin and triple 2 strokes to 250cc and all 4 strokes up to 500cc. This class, like the other two classes in Portuguese classic racing, is very poorly supported, which is a pity as they have good circuits at Estoril, Braga and Portimao.
As regards the discussion on replicas, I had a '1962' 500 Manx up until '72 (don't ask!) and now run a 93 bore replica, and I know which is quicker, safer and more reliable. I love it, complete with belt drive, Mikuni carb, Interspan ignition, titanium valves, nicasil bore, Dunnell frame, twin plug head and everything else. But then I had a Norvil disc on the Manx back in the day - must be me. (And I painted the frame white)
A chacun son goût. A safe 2015 to all.
Tom