Do you have the tail cone attached or the gear legs? If not, leave them off for now. You have it a lot easier to do the retrofit if you have access to the rear of the fuselage from the tail cone side. Also it would be desirable to do the wiring while you can still turn the fuselage on its side and work in the tunnel while you're comfortably seated on a little chair.
There are not a lot of changes to the wiring but the routing is tricky as the snap bushings are pretty tightly filled. Doing the wiring all at once might be more enjoyable but the main thing really is the fuselage on side option as well as not having the tailcone making drilling in a flange of the fuselage aft bulkhead trickier.
