Perhaps, and maybe it’s old wives tales. The suggestion was the RF could damage ecus in the vehicle.

And to think back in the day I welded an inner wheel arch into my old classic rangie whilst the lpg tank was sat across the boot between the arches inches away from the weld … it’s a wonder I’m still here sometimes

Had a look on the micro part diagams … the chassis sections that the subframe joins to are quite large pieces. You’d have to cut both the old and new to get it to a size where you could weld in a new piece.

I almost wonder it a better approach would be a piece alu billet machined to shape would be better As you need threaded holes for the big bolts of the subframe. . V8 or else ...