There is another possibility that rears its head with front brakes --- many calipers can be switched left-for-right, and will bolt up just fine --- but the bleed screw isn't at the very top of the caliper (if installed on the wrong side). So a pocket of air stays at the top of the caliper and ruins your attempts to bleed the calipers and lines. I may be incorrect that left and right calipers can be installed on the wrong sides on a 123 --- but I did it on Crown Vic wagon and scratched my head for some time before realizing why the brakes wouldn't bleed successfully.

It's easy to check ...