Brian is correct about height required to get even seven pounds injection pump base pressure. Since it has been established these cars will start and run at lower injection pump base pressures. For example some have removed the relief valve spring and their cars started. Fair to state as well that some pressure was perhaps available in the pump as the return orfice on the relief valve is small.

Others have watched their available base pressure drop to basically nothing when accelerating on the highway with a gauge monitoring the fuel pressure.

A modest elevation at least is still indicated for a gravity test. It does not have to run perfectly with this setup just catch and run easily. That would still prove or eliminate the fault type in my opinion.

You are right a length of fuel hose or something equivelant would be required. You are trying to supply the injection pump directly. Or a piece of your old fuel line and a rubber coupler for example. You may still have what you already changed out for example.

It just occured to me as you say the primer pump is still basically functional. A simpler and perhaps more or less conclusive test might be to pump the primer pump a lot just prior to trying to start after a prolonged down time. Hopefully expelling any air through the relief valve that may have accumulated as you get fuel flowing. Leaving the return line off the relief valve on the injection pump may increase or aid your observation of when solid fuel is flowing. Then screw down the primer pump handle and try a start.

I really like to keep things as simple as possible when troubleshooting. My limited intellect demands this appproach.