flying2bill
I have two of these such convertions and love them.
They are posted at rcwarbirds.com and the twinman posts. I use the spacer, because it was easier to build the wing without plug-in's.
Plan on a rat's nest of crossover wiring each time you get ready to fly and make sure you can support the two fuse's during wing installation to not stress the horizontal stab...been there done that!!!
Do consider to link the engines electrically to the rudders. Really aids the knife edge and getting out of spins!!!!
If you have any concerns about the structure of your wing, lay a small strip of carbon fiber the entire lenght of the wing..both sides, as you will do many manuvers stressing both sides of the wing.
Good Luck