Worth mentioning the exhaust for mods. A free flow, decat exhaust paired with good headers will bring some more BHP to the table. Again, just like the cams, it will move the torque upper in the revs, making it feel less torquey bellow 3k.
Regarding the displacement mod, 330i crank, rods and pistons into M50 block: is this a straight swap? I mean, it's just a matter of removing old crank, rods and pistons and fitting the 330i ones, or is there something else to be aware of? I've heard of this before, but sounds too easy (and good) to be true.