I have sprayed 10 + sets of crankcases using the aerosol tin made by Holts and available in the UK called " Simonise 5 Wheels" check out the link:-
http://www.holtsauto.com/hints/index.htmlOne tin does a set of cases, no special prep needed, it does not react with other paints. It never goes off color due to petrol ( its designed to withstand brake dust + heat ).
Best preperation is wire brush/400 grit wet and dry then warm the cases to 40 deg. Put the spray tin in warm water for 15 mins. Blow off any water round spray nozzel before use.
Its so good you can degrease an engine, warm it up mask it and spary in situe.
Oh update 12/04/07 just found out they make 2 colours now, it's obvious which is which (I just sprayed a top crankcase in one tin switched to another tin for the botton case and found out) there is a darker one as well. Get the light one for Honda cases and the dark one matches late Yamaha.