Ok going through mocking up the 42 Tudor. New Bolt in parallel leaf spring and Mustang II (thinking it came with one or the other but just don't know) Got two of these plates,about 6" x 3" and can't for the life of me figure out what they are....long shot I know but worth a try.
They are for bolting something a little narrower to something a little wider! Sorry just had a shoulder operation, it must be the drugs!
I would guess its for the mustang II ifs. I have a 48 and when made there were a lot of about 3" holes in frame. I guess its to go behind cover the hole and bolt to cross member