Sorry it is the piece that goes by the gearbox, I probably got my terminology wrong! It is the shape that is unique to early bays with the removable rear valance.
I have the piece that attaches behind the pully which you can only remove when the pulley is off - if that is what you are after.
If you are after the piece that the heater hoses go through then I'm afraid I can't help. Sorry.
Please let me know your address and I will post it first thing tomorrow.
I didn't use that piece as it didn't arrive until the other piece I had did, and I was waiting on the front tin desperately and so used the first piece that arrived!!