so you do think more testing is required?
Let's start over.
Your plumbing should be as follows....
from the jet pump directly to a several turn gate valve.
from the gate valve directly to the front of the engine where there used to be a water pump (if memory serves a BBF)
from the t-stat housing (with no thermostat installed) two hoses, one to an overboard dump fitting approx 3/8" to 7/16" opening and the other to a header control tee, sometimes a 1/2" ball valve will/can be installed directly before the header control valve.
If you over pressurize a Ford, there is an excellent chance you will blow the ends of the intake manifold gasket on the inside of the lifter valley causing the banana delight smoothie...

This would be where I would check first.
If/when you pull the intake, it is important that you be sure to seal the gaskets around the water ports in the heads very well. this is the weak link, especially on an aluminum manifold.
I have successfully used Permatex number 2 ( the soft gooey chit), contact cement, Ultra Black RTV and Spray Tack.
How long did you pressurize the block with the stat hoses blocked? It should hold 15-20 PSI air pressure for a damn long time....

Like enough time to eat a sandwich and drink an ice cold beer....Minimum...I have seen them hold pressure for over a week.

Good luck....

GT