Its squeeking means it may now be working. The question is at what pressure does it open and does it seal properly when closed. The primer pump gets a little harder up to the point of the valve opening. Then the push pressure remains constant.

A lot of the time the presence of any air is modifying the feel of the primer pump until it is expelled. I do not think you had air to contend with or very little. So your push pressure just might be right with no air.

When you clamp off the return the output from the injection pump base is effectivly closed. You cannot pump fluid in a closed system. Fuel like all fluids does not compress. Kind of a general statement there but okay for our needs. The primer pump cannot basically be moved if everything is right. You call it very hard and it would be in that senario.

I would try starting the car now. It may suprise you. I think it will run. Or until your parts arrive why not read the relief valve spring thread started by Cervan. With a little luck you will get through it before your parts arrive.

Anyways I think and hope your problem is now resolved. I would post how this engine runs sometime. Your experience to me indicates it may be a candidate for further improvement with no or very little money required to achive it. A lot of these cars have experienced neglectful maintence if any over the years.