Raybo, you need to post the Model number of the Nissan forklift you are working on. Then someone may be able to determine precisely what V/R is supposed to be on this truck.
I am leaning toward MEngr being correct in stating that a Model J Impco is what should have been found on this truck.
You stated that on the Model L V/R there is a solenoid 7007B.
7007B is listed as a Fuel Lock Off valve. All the old school LPG systems I am familiar with used EITHER a vacuum operated fuel lock (such as the VFF 30) or an electric fuel lock (such as the 7007B) but not BOTH on the same application.
Discovering a VFF 30 AND a 7007B on the same truck smells sort of like somebody has done some "cobbling together" with spare parts at some time past.
For safety and convenience/dependability you really need to get the truck back to the components it is supposed to have.
For the interim period you guys should practice the recommended procedure of turning off the LPG tank hand valve when the forklift is parked.
Turn off the tank hand valve while the engine is running and then run the engine until it depletes the fuel in the plumbing.
Doing this should provide a temporary solution for your having to remove the vapor hose for cold starting.