You're right Don, but I think the original question was if a lightweight F40 bike could compete in heavyweight F40. The answer would be yes, but only if it was a production street bike prepped to supersport rules. The rules for Heavyweight F40 require supersport trim, so the lightweight bike would need DOT tires, stock displacement, airbox, ect. to be run in the heavyweight F40 class.
In lightweight F40, anything goes as per lightweight superbike and lightweight GP rules.