Been there, done that...
The head is the biggest visible difference but the carb is what going to give you trouble.
If you were putting a heli eng into airplane, it's not a big deal. You would end up with a rich midrange and maybe a flame-out or two until you got it dialed in.
The airplane carb is leaner in the mid range than the heli causing you to run the high and low needles rich to compensate. I'll load up while idling and drink fuel or die when you punch it. If you run the needles normal, it'll be lean in hover, very bad for an ABC heli eng.
You may be able to change to the heli low needle to get the extra fuel and put in a thicker shim to get the C/R down.
For what you spend on a head, needle and your trouble, you could get a .39 for your chopper and save yourself the headache.
Oh ya, once you cut the crank off shorter to fit the heli, there's no going back.
Kirk