Well it looks like you have made up your mind!!
First thing is that you are going to have to beef up them rear stringers to take the load!
Next I think you are also going to have to widen the engin box, cause its going to be tight!!
Look at this thread, Cliff just repaired his rear stringers and reinstalled a motor
http://www.wellcraftv20.com/cgi-bin/...852167;start=0
When you get started take lots of pictures, and start a new thread so we can follow along and help were ever we can!!
Good Luck!