This can be done but you need to realize that if your going to use castiron heads you will need good valves 2.14/1.81 good springs keepers and retainers. Cut the open chambers down to 80cc closed down to 70cc pocket port and do a performance valve job if you can find a good set the aren't cracked. Your going to have close to a grand in your castiron heads that don't flow. You also need a cam with more duration to make work than the new aluminum heads.