This may help, but I have a 71 Demon that came with a 318, 3 speed. I put a 4 speed in it, and all I did was take out the 3 speed, put the 4 speed in. Only thing that was changed was the rear yoke in the trans. Everything else remained the same.

Bell housing should stay the same, again not an expert on I6, and the biggest clutch would probably be the 10.5.