Just found my copy of the photo- mine says" factory built lotus seven eleven". Do you have a photo of the front?
You've found it! I don't have a photo of the front. The photo appears on a dedicated Lotus 7 site and is in a section of unusual bodywork. The owner of the car fitted the rear end of a Lotus XI for some reason or other. I didn't think it was factory fitted, but it's possible.
You've done enough for the point.
PS I've just found your source and it does seem highly likely that this bodywork was fitted at the factory, because that's where it was photographed. It's chassis #465. Presumably a special order, although a later owner removed it and reverted to the standard bodystyle.