39 Plymouth truck

Hi all. My 39 Plymouth pickup truck PT-81 (flathead 6) is getting increasingly hard to start when cold. Once started and warmed up it starts to stumble and backfires when I try to rev up or drive it.

Have installed carb spacer, electric fuel pump, carb heat shield, I have done complete tune up with new parts, coil, fresh gas etc.

Any ideas would be greatly appreciated as I cannot even drive the truck anymore...gordyc