dhjmd,
The intermediate fitting, as you refer to, is included with the classic parts petcock. That is the verticle pipe in the picture that is threaded into the valve and threads directly into the tank. If that doesn't fit then klhansen may be correct in that some repop tanks have metric pipe threads. If that is not the case then perhaps you could chase the tank threads with a 1/8 pipe thread tap. There are no other parts necessary to reproduce the factory fuel line out of the tank. Let us know how you fare.
Kent
