I finally got around to fitting the petrol filler in the moulded hump as per the original.
I simply routed two lengths of 50mm stainless steel pipe which were plumped to the original Scimitar tank inlet using three 90% silicone bends.
The hatch that cover this rear end will now need to be trimmed to fit.
I was going to bond the cover on permanently, fill and smooth out the gaps around it but now think it will look better and be more practicable if it's removable as per the original "D" type.
