Alright, first thing's first - mounting the gearbox in the car. Andrew from Zero to 60
explains well in his YouTube video that neither an F30 8HP45 or E9X 6HP19/21 mount will work. In my case nobody has documented (to my knowledge) going from S6-53 to HP70, so tonight I pulled off my S6-53's bracket to see.
Not a chance. This one seems even smaller than a 6HP bracket. I've ordered a 6HP28 335d bracket which should bolt right up on the 8HP70, and will have it either tomorrow or Monday to test out. The only question mark is whether or not the mount spacing and keys will fit up to the manual cross-member. Time will tell, and hopefully the front-to-back spacing is good too. Time will tell!