Good job on the window. Pretty creative.
If you had the intake manifold leak after the CAT was replaced the first time it is possible that the CAT was damaged. Not all coolant gets burned off in combustion so some will work its way into the exhaust system. The CAT operates around 1200 degrees F when operating properly. Antifreeze will cause the CAT to exceed these temperatures and it will damage the CAT. Misfires wil also damage a CAT.
DTC error code P0420 is normally a bad CAT and to have a bad CAT again is a possibility. If the error code stays off for several drive cycles with the new CAT then you'll probably be OK.