a metal tube that runs along the frame on the passenger side in the engine compartment. hooks up to the firewall. i think it is for the heater. i don't know what it is called to replace it as mine is rotted out. it is #2. i don't have tpi, just carb, so do i need it or just run rubber hose.

 

Yeah, it's for the heater hoses. Serves two purposes, first it returns water from the heater core to the radiator, and two it also is used to run the water from the intake directly back to the radiator if you are bypassing the heater core with the heater valve ( part 5 in the pic) Whether or not you need it depends on if you still use the bypass valve for the heater core. If not and you still use the heater core you can replace it by just running a hose from the core to the radiator, and the water outlet on the intake to the intake side of heater core. Or if you don't even use the heater at all. just go from intake back to radiator and skip the heater core

 

In most inventory lists it is just reffered to as "pipe to..". If you want your car to look stock, you can definitly find it online somewhere or even remove it and take the pipe to a machine shop and have one fabricated. Good luck to you.

 

any junkyards around? you can pick one up there. some people bypass the heater control valve. which i guess is an option for you too and you can run rubber.