I have those M/T cast covers on my Eddie headed 360 with an AirGap. I had to notch the covers to go over the AG runners. No leaks.
It is fairly easy to pressurize the entire engine with a regulated air source, through the dipstick tube. The breather ports, and the PCV, have to be blocked. I use 4psi. Then a soap and water test will find the leak(s).
If it blows the dipstick out,or spits oil out the breathers, you need to perform a blow-by test. The PCV system cannot keep up to bad rings at very much throttle/load settings.It's only there for light throttle and cruising, really. At WOT it backs up and usually exits into the air cleaner housing, where the oil(if existing) condenses out, and the air goes back down the carb throats, and at idle it sits on a minimum bypass disc.
In your case, the breathers need to be open in both directions, so WOT blow-by can exit there. If they are one-way check-valved, the engine will be pressurized at WOT and it will find the weakest places to blow out. Most/All engines will exhibit some pressure into the crankcase at full-load WOT.
So pull the breathers out and blow hard; making sure they are two-way breathers.
