Not all my readers are on Facebook so i thought i would post back some information I posted on Facebook so you can all see it. Its in response to a few questions from a 2.6 Lotus engine owner, I hope it adds to the greater knowledge and is interesting to those who like that sort of thing.
Below are two images of the heads, the first shows the Lotus heads, the production 907 head and the development 907 head.
Its clear the development head is much more like the 2000cc Vauxhall GT head in terms of its shape and waterway design. What I do want to point out is the oil-way location, which is totally unique to the head and ultimately the block. God help us if the head or block ever get separated.
For reference I have added a second image of the vauxhall heads.