JP110,
The one on the left is the correct one. I install that one on my 04 900 - it goes in the frost plug at the rear of the head. The dealer should have supplied an install sheet w/ the part. I still have mine - of course drain the coolant. remove the frost plug & clean the opening. I painted mine w/ hi-temp paint prior to the install. Use some type of sealant that u like. Use a 1 inch socket over the treads to protect them - the socket will rest on the shoulder of the heater. Use an appropriate persuader (hammer) to install heater until the other shoulder makes contact with the head. Because I had the coolant out I also added a lower radiator hose heater (from auto parts store). Refill, run, and check for leaks etc. I routed the electric cords to the left side of the engine bay. I mounted a 2 outlet fiberglass electrical box. Wired in the outlet to a single cord - which hangs outside the left frame rail. The 2 heaters are plugged into the outlet. So, when it's cold (it's damn cold in MN) I just plug in the 1 cord to turn on both heaters. I'll try to post some pics - soon