With enough money, time and motivation you can do just about anything, no matter how crazy. Apart from simply proving it could be done, why would you want to do this?
Having said that, you'll need serious floor and tunnel mods, which could well lead you to an engineer. A trimatic will certainly bolt up to a 138 red, and will probably fit a grey - after all, you can bolt a red to a grey crashbox, so it's feasible to bolt a grey to a red slushbox I suppose
You won't need a pressure plate, though
Before spending any money on this venture, see if you can get a ride in an original EK or EJ automatic. Not exactly a performance powerhouse, are they? :-/
cheers
RET
PS I have fitted a 186/powerglide combo to my FE, so I have some experience in this area. I like it, but I wouldn't do it again.