Tim,
I agree with Morgan, 1985 or 87. No full bodywork.
A lot of it depends on the engine. Here is the AKRA Enduro Vintage class description:
Vintage Piston Port/USA Final 1; Final 2
Competition Age: 15 and up
Engines: Any American made, fan style kart engine (100cc and 125CC McCulloch, 135cc West Bend), Or Non Fan – Yamaha KT 100, ARC, Dap T-50, TKM BT 82, PCR PP-100, PRD (Stock Only)
Weight: No minimum weight
Pipe: Any pipe, Horstman is the only wet axle clutch allowed, all other clutches allowed.
Fuel: Open Fuel
Vintage Unlimited Final 1; Final 2
Competition Age: 15 and up
Engines: Any 100cc–150cc. (Open Modifications, Any Carburetor allowed),
Weight: No minimum weight
Pipe: Any pipe, Any clutch.
Fuel: Open Fuel