Just bought a new parts store radiator for my 73 work truck (400).

Installed and found the inlet on the opposite (left) side. The new Rad has an emissions fitting on the right boss where the '73 would normally have its hose.

I figure they probably made a design change at some point in the 70s when they started adding emissions to trucks. Thus if I ordered a hose for a '78 big block, it should fit both the thermostat side (since that never changed) and the radiator side.

Make sense?