You are not experiencing vapour lock. If you were, the car would stall. 'Vapour lock' is not a catch-all term for heat-related fuel system hassles; it means only one thing: a big vapour bubble encompassing both sides of the fuel pump, caused by excess heat transfer to the fuel line. There is no liquid fuel available at the inlet of the fuel pump, so there is no liquid fuel pumped to the outlet, so the engine won't run. Not a match for your symptoms.
What you are trying to solve with heat shields and fuel line reroutes and suchlike is percolation, the fuel boiling in the carburetor (and/or in the pump-to-carb line) which results in an overly-rich mixture reaching the cylinders, causing rough running.
You can also "buy" your engine some additional leeway for dealing with less-than-perfect carburetion by following the tune-up parts and technique suggestions in this post, and by upgrading the ignition system.
Why do problems like this exist? it's true that today's gasoline is different to the stuff available in 1974—in most ways, today's gasoline is quite a lot better, but carbureted-engine driveability is not today's top priority in gasoline formulation, because most vehicles do not have carburetors. But leaving that aside, driveability of even a brand-new 1974 carbureted car was imperfect at very tip-top best. Take a look at this 1973 Chrysler video—12 minutes of what to do about poor starting:
Exactly none of this is of any concern with fuel injection; just hop in, turn the key, and drive off. It's not just starting; the same applies in pretty much all other conditions—idle, acceleration, cruise, etc.
