Cam/Head Swap Disaster.......

That is some excellent advice on the water removal, I too was thinking non polarized (I.e. alcohol) for flushing. E98 fuel would work too. It’s not my decision and I understand time and cost constraints, but with all the possible problem areas you need to look at along with the time combined with labor intensity of getting the water out and front cover accessibility, I would consider pulling the engine and doing a partial tear down and spray out with alcohol and diesel with the pan off, valley open, and valve covers removed. But that’s just me, and I am really hoping for the best on this one. You may want to check out the Hughes racing engine site on the tech pages about intake manifold sealing too, but it sounds like you’ve got it pretty well diagnosed. I use lead from tire weights instead of wire wax to check clearances, but I do use that procedure.