The only '68 US models to use that style of front fender and front loop stay were the Spitfire and the Firebird Scrambler.
The only '68 US model to use shouldered alloy rims (Borrani) was the Spitfire. The OP's rim is a Borrani.
Th OP's image has standard pipes, not high pipes of the Firebird Srambler. As a result, I assume, unless added to another model, the bike is a Spitfire.
The OP's loop stay measurement is correct for the '68 Spitfire (& Firebird).
Fix or replace the center fender bracket, position it correctly, and the fender will be positioned correctly.