OK from the WERA rulebook
CLUBMAN EXPERT & NOVICE (all below based on Formula rules except as noted)
Unlimited displacement 2 & 4-stroke singles
Up to 605cc 4-stroke water-cooled twins
Up to 650cc 4-stroke air-cooled twins
Up to 250cc 4-stroke water-cooled multis
Up to 600cc 4-stroke air-cooled 2 valve per cylinder multis
Up to 570cc 4-stroke air-cooled 4 valve per cylinder multis
Up to 450cc 2-stroke air-cooled multis
Up to 396cc 2-stroke water-cooled multis
All Vintage 3 & 4 machines
*Honda Hawks and Air cooled Ducati 750ās, 250cc 2-stroke GP replica machines (TZR, NSR, RGV, etc..), Aprilia Cup, and Triumph Thruxton, are allowed but limited to Superstock mods with the exception that slicks are allowed., no Ducati Supermono. 125cc & 250cc GP machines are not allowed.
Formula 500
Pre 1973 2-stroke factory road racers up to 360cc.
Pre 1974 2-stroke production machines up to 500cc.
Pre 1974 4-stroke, 4 cylinder up to 500cc.
Among the eligible Formula 500 machines are the following: Bridgestone 350; Cagiva-Ducati 500cc Panta twins; Honda CB350F, 400F, 500F, CB450 and 500 twins, CB550 and 1977 MT125; Kasawaki H1, H1R, and S3 400cc; Moto-Guzzi 500 twin; Suzuki 500 Titan, GT 380, GT550, and GS450 any year up to 550cc; Yamaha RD350, RD400 (regardless of year), R5, SR500s (up to 540cc), TR2, TR3, TZ 250 and 350 (twin shock, no āGā model cylinders). TZ 750 cylinder and head (model 409 only) may also be used. The use of cast wheels is allowed in this class.