one of my lasts posts :(
have a look at an early narrow body westfield independant setup (up to about 92ish). westfield made there own casing for the english diff which is really small and light (ali casting). if you can get hold of one of these then that would save a lot of space and mean you can use your existing diff. chassis mods for this diff should be relatively minor. i also think you will be able to use existing fuel tank.
email me and i might be able to get some photos. alternatively ask on the wscc boardroom.
i know v7 looked into this, but i think he ruled it out 🤔
hth (for now)