And are the scratched, sorry - nicely patinated, edges of the dumbiron apron due to it falling off and you running over it? My car has similar patination, acquired in that particular way over the years.
Well spotted, Brian, and caused exactly as you describe on the UVCC National Trust rally earlier this year. Fortunately the hold down bolt ended up in the road beside the valance so both were quickly gathered up and stowed at my navigator's feet until the final time control.
I purchased two lids for my J2 from Burlen about two years ago just like the ones you are looking for. I believe they are 1 1/2" diameter without going out to the shop to measure them. The original ones I have have bad threads where the fuel inlet fitting goes and one lid has a broken piece for the pin for the float lever. I was very happy with being able to get new ones although I'm one who would usually prefer original parts. Sometimes a new/reproduction part is our best or only choice.