It would be a pretty major modification.
There are quite a few differences in the fuselage fwd of the main wing spar center section.
 
You can change a nosewheel in tailwheel. If so, how much approximately?

What model are you thinking of converting? I called The Factory and asked about converting an 8 - they said it was a huge project, and they wouldn't do it themselves. I know someone on the forum has done it, but it is a very major undertaking. The one I am thinking of wasn't to the flying point when the conversion occurred.