I looked into the mod a while back and gave up before i started. It was going to involve alot more modification than i thought it would and gave up.
You are going to need that basic clutch setup for that engine and and probably a 14 tooth clutch bell.
If i was you i would contact Matt at
http://www.ballistictechnology.com/
He makes a lot of upgrades for the Corona (electric) but if you e-mail him he might very well make a custom crutch and gear for you.
That is probably you best shot.
I would also seriously consider pricing a larger heli
Good Luck