The Tokheim 300 uses 2 different types of receiver. If your pump has a crank handle to reset the computer then the nozzle receiver uses the paddle type nozzle rest. If your pump has the dog bone lever under the nozzle then you have the model 56 semi auto reset computer (does not have a crank handle opposite side of the nozzle.
The fiberglass nozzle boots are hard to find with the end still in them. The tip of the nozzle usually breaks out the fiberglass.
I know I have the auto reset version, would have to check on the other.
Tom.