Lots were using So.Cal frame builders Executive Tool and Die to make all the dropouts and Brake Plates back in the 80's.
Supercross used GHP shape dropouts on F&F for 2 reasons, GHP was out of business at the time they started making frames and Greg came up with the name so Bill chose the GHP tooling as homage too. Forks are often National Pro Fork Dropouts which are still used.
Common for the dropouts and tubing to be used with good fabricators just putting them together with customer angles and specs.
ELF were supposed to build Bills first frames but let him down then the Shoups (BOSS) helped out with the prototypes.