This is the way I think your path should be.
Your pump flow is going to the hyd block, so the out of the hyd block should go to the FEL, and after you install the correct PB adapter, run a hose from the PB port to the valve block. The fluid from the valve block will then go to the 3pt, and then to tank.
The return /OUT of the FEL should go to tank.
You probably need to set the FEL relief to about 50 to 100 below the pump max pressure.
This is a sleeve type PB adapter. The other PB adapter is a hex screw.
If that is an PB adapter in the end of the valve, and you put a plug in it, then you made the valve a closed center valve. If so remove that plug and connect a hose from the PB adapter to the valve block.
That would also block the fluid and cause the relief to dump/squeal, and build up heat if it stays that way. And yes, when you use the FEL, the used fluid is going to the out port, and the squealing stops while you are using the FEL.
Use air to check out the flow through all the valves.
What you have said and done is all logical, but not necessarily right.