Aye, the fun is really starting now.
I needed to recreate the flange on the tie plate to be able to properly fix the flitch and inner arch and at the same time provide a seat for a strengthening gusset to support the bumper mounting bar so made this dual purpose 3-D sculpture from 1.5mm thick steel.
This doubles as flange and seat and was made from just 2 pieces. It's designed to sit on top of the tie plate as a doubler yet be flush with the existing flange where I cut the rot out. It just needs the flange reducing a touch and it's ready to go in. Parent panels now need every trace of paint and underseal stripping from the area before I weld in this first of many fixes