As for the tranny, I think people underestimate this ZF tranny!
It's tested and maxed out at 546 ft TQ !
That means its fairly safe for huge amount of torque. 335i ZF are rated much less than that and people put 450-500 TQ on theirs without any issues! Look at 335i MRC, they have almost 550 TQ at theirs and its no diesel!
I believe our tranny can support up to 650 TQ