Which fuel pump should I use?

I have a 1996 Chevy Silverado PU that hasV8 vortec engine in it that will not start, we have pinpointed that it is the fuel pump, my problem is that the VIN shows the truck should have a V6 in it and the motor is a Vortec V8 (the perils of buying from honest car salesmen). Anyway, I am not sure which fuel pump. Technically, it should be the V6 pump in the tank, but, when a motor is changed is a fuel pump change part of a new motor? I know I am swatting at flies with this, but wanted to run it by the community before I had to take the bed off of the truck. (the gas tank is full, so taking the bed off probably the least difficult route). The two pumps are completely different, and the prices reflect that. v6 about $50, v8 about $240. So, thanks for reading this, I really appreciate positive feedback! Thanks and Happy Holidays!