What was the issue with the FP gauge?
You could use a standard fuel pressure tester tool kit that has the gauge on a hose and includes a tee to put near the carb inlet, shim the hood hinge up enough to run the hose out to the windshield, and duct tape the gauge face to the glass. Could also use a $20 usb borescope cable camera plugged into your phone.
I'm thinking tank sender too. I believe they make a high flow version.
Might also loosen the gas cap and reinstall right before a test with to see if it makes a difference. The fuel burn rate at WOT may exceed the one working vent's capacity to let air in.