I did it 3 yrs ago. blew an 03 bought crashed apex. Built a 1100 cc stroker out of it. you need all of the electronics including the fuel injection, electric fuel pump, and speedometer pod oh yea and the handlebars or warmers off an 06 or later.
Its not worth it unless you can find a totalled one for under $2k which is impossible. I paid $3500 for the sled and without stroking it would have spent another $1500 to have it gone through. Other than throttle response I don't feel that the seld was any faster and I could have bought another RX in 05 mono for $4k with 2K miles on it.
I spent $4K to have the motor built, did all of the rest of the work myself and it lasted 3500 miles (2 months) and threw 2 rods.