It's a pity that original Mk1 drawings still do not seem to be available to the general public.
Making do by combining information that is may fill that void to some extend.
I've superimposed a (fragment of a) drawing of the original Mk1 over the Mk2/1 drawing that SNAFU22 posted to make visible the differences between them.
(black lines are Mk2/1, red lines are Mk1 double dovetail)
It looks like the overall contour didn't change much; most of the lines overlap or deviate only a little, mostly due to folds in the scanned drawings.


This certainly helps to validate my assumption that a drawing of an Mk2 could well be used to reconstruct a drawing of an Mk1, which I did here:


In 3D that comparison looks like this:


Hope some of you find these images useful.

Cheers!
Erik