Im gonna go against the grind here.
I personally would recommend just buying the RN and being done with the ordeal.
Buy the RN for $2500, list your SN for $1000-1500 and only still have roughly the same amount "invested" as if you did the motor swap, but yet you would have a RN ski instead of the SN.
Just my opinion. If you are wanting a RN now, you will still be wanting a RN later even if you have the bigger motor in your SN.
Oh..and if you do wait and decide to just upgrade your SN to a 701...remember that down the road you will easily have $1k into a nice hull with the other stuff. I bought my RN hull for $700, however still had to get a hood seal, pole bracket, pivot bolt, all steering and still looking for a reasonably price RN waterbox...probably just going to run the SN one.