I am switching motors in a 1984 Chevy pick up.

You're best bet is to go with a low-pressure electric pump. 3 - 5 pounds would be typical.

The newer engine might have the same timing chain cover with a fuel pump block-off plate, but since it didn't come with the pump bolted there, there is not going to be the eccentric on the camshaft to run the pump. Switching enough parts to to allow installation of the mechanical pump could get to be real involved, and since there's such a big age difference, it's impossible to know what will interchange and what won't.

Keep in mind that mechanical fuel pumps obviously stop working when the engine stops. With fuel injection systems, the Engine Computer gets involved in turning on the electric pump. That is so it will turn off in the event of a crash that ruptures a fuel line. The engine can't run without fuel pressure. When the computer sees the engine stopped, it turns off the fuel pump relay. That prevents raw fuel from pumping onto the ground. You will want to incorporate the same type of safety system. The easiest is to install a tee fitting for the oil pressure sending unit, then add a low-oil switch; the same used to turn on a dash warning light. Connect the fuel pump's positive wire to something under the hood that gets 12 volts when the ignition switch is on. The ignition coil is a good candidate. Connect the negative wire to that low oil pressure switch. The engine will start and run for a couple of minutes on the fuel in the carburetor's float bowl. The oil pressure will come up within a few seconds of starting and that will turn on the fuel pump. When the engine stalls, for any reason, the fuel pump will turn off.