I have rebuilt a few Morgans in my time (admittedly not a 4/4 4 seater) but i have never come across any wooden panel that looks even remotely like that.
However perhaps someone familiar with the 4/4 Series 1 may be able to rule out that this is not part of the bulkhead (which are wood)
John Merton would know if anyone does, his knowledge of Series 1s is encyclopaedic.
Personally, I'm pretty convinced it's not from a 1970s Morgan
