I went to every hardware store around here and the only thing close to what would fit is a rubber tapered plug, however, I test fit it and there is barely any clearance to clear the flywheel.
I was thinking to RTV a large 1/2 washer over the hole and JB weld the hole on the washer shut, any objections?
Update from dealer:
Service advisor received a letter from Ford corp "engineer". Letter "email" states no reverse is from motor swap install. Ford engineer recommends putting original motor back in.