I am all for Turbo charcghing an M10. Someday I would like to turbo one of two M10 engines I have sitting in my shop.
Bmw did turbo charge a 2002 with an M10 2.0 in 1974. If you could find that exhaust manifold it would make things easier, since the manifold is meant for a turbo.
I would also use an engine from a 1977-79 320i. 1979 was the last production year of the 2.0 M10, after that they only made the 1.8. And those years of a m10 also has a double row cam timing chain instead of a single chain. Also use a good aftermarket fuel injection system like the Motec or similiar brands.
The bottom end of the M10 is really strong. If you start building serious horsepower and boost you will probably want to beef up the bottom end. If you want to go real radical you can cut the 8 counter weights off the crankshaft, have it re-balanced, through some after market connecting rods in it, and then it should handle a lot of boost and power.
Just my opinions. I want to play with an M10 someday when I got the money. Be fun to have an old school 8 valve 4 cylinder bmw blow away the new rice rockets.