One possible source of chrome plating might be the local custom motorcycle shop, if they don't do their own chrome plating, they send it out to a plater, , and could hang a chassis or two in the same batch as their motorcycle parts. It won't be cheap, but the workmanship and quality will be excellent
Harley riders LOVE their chrome, and they want it thick and shiny
What you might try, is to cover the chassis top and sides with the blue "painters" masking tape, and do the marking and drilling with that on the chassis, and then peel it off after you're done. It should protect the chromw plating form any scratches, and it is a LOT easier to mark than the bare shiny metal. The advantag of the blue tapeis that it peels off very easily afterwards, and doesn't leave sticky resiidue like the white masking tape does.
/ed B