The following week, I welded the replacement section in place and then grinded...a lot!
I also prepared the second replacement piece out of the aftermarket wheelhouse that I bought to serve as a donor supplier of repair sections. I also had to recreate a small section of the inner wheel house edge that the overlapping "flap" mates to. (All that crusty black stuff is old undercoating and will be scraped out of there soon).
And here it is after some minor body work and filler:
as compared to the opposite untouched side:
