http://www.e30m50.com/
http://www.lukasbmw.com/m50_swap_advice.htm
just a couple that i have found.
in the first site, i think they tell you what resource to buy in order to have all the parts needed.
the engine swap is a great idea if you are willing and capable - the m20 doesnt support more than 200 hp without lots of money and tuning.
plus i suggest m50 tranny as well, the m20 will work, but minor modifications are needed, m50 tranny, its just bolt and drop in bay.
PLEASE update us if you find other resources, i am very interested in this as well.