on regards to the paining of the engine, in my opinion id first atack the engine fines with a file squaring them of with the file to make a nice flat face on the fines and giving some cemantary to the cyl and head then get a fine file and smoth it all down then go through some polishing proces to makle em shine (just the out side edge of the finns.. then take all the side covers of the motor paint the engine satin black,, for a factory look have some thinners handy on a rag and wipe the polished fine edges clean ,, now go and get your side covers polished to leave a lovly polished alloy look.. get some nice black allen key bolats and bolt it alltogether this will then of set and complement a nice black engine with shinny alloy accents to your black cruser and will look alot better then a out of the box flat alloy motor..
just a suggestion but i think it would look majic in your bike..