I want to convert my 88 from TBI to carburated and I was just wondering if I can put a mechanical pump on it. I notice that there is a block off plate on the block where the pump would go, but I was just wondering if the EFI trucks had a lobe on the cam to drivea mechanical pump.And will the stock cam even run with a carb?

I would use the pump that is currently running your injectors. The pressure will be to high so you will need a pressure regulator. The chances that there is a fuel pump eccentric on your fuel injected motor is very slim so that means you will have to pull the timing chain cover and install one to use a mech. pump.

I plan on doing a cam swap later, so that may become an option. But for now I think maybe your right.

I recommend a bypass regulator so you don't burnup the pump.You still could have a eccentric in there,the cam will run ok.
Remember this is a computer controlled motor so your computer will be confused and may play havoc with your timing.

The computer is going bye-bye. I`m going to rewire the whole truck.