Quickly taking a screen shot of Erik’s images (which hopefully are to scale with each other), Mongo overlaid one on the other.
1.4 III - dark rose coloured elements with grey body
1.4 II - pink coloured elements with dark body
You will see from the edited diagram that some things line up and some do not. The rear mount lines up on one side but not the other. This must be an error in the diagram because the rear mount is perfectly parallel to the body. So, there is some diagram error or distortion in the proportions or the scale somehow. It is difficult to know what parts may be just housing and not the mount itself.
In Mongo’s view, you must be able to:-
1. transplant the whole of the version III elements and groups exactly as they are.
2. ensure that the front and rear elements of the converter are exactly the same distance from the front and rear mounts respectively as they had on the Version III converter
It looks like you can fit all the version III elements/groupings into the version II housing IF you can overcome the slightly smaller housing at the front of the converter. If you can, then, it seems possibly to get that front element the correct distance from the front mount. However, it looks like the rear element will protrude a little too much from its required distance to the rear mount.
A lot of this is pure speculation without having precise scale diagrams and measurements.
Last point .........is it really worth this incredible trouble