I just did it with a 1300. Like others mentioned you have to do a modification for the auger motor which was the only mod I needed to do.
The previous owner was shipped a new D2 controller from Traeger even though it was the D1 AC version. He couldn't do it so he gave it to me. I bought the auger motor, fan, firebox/hot rod and auger. Since he already had the most expensive part (controller) I am in it $300 and time. Works great and the grill itself was practically new so a good deal in my opinion.
I later bought the thermocouple because i broke the tip off the original.
I also just bought the pellet sensor since the D2 has the plug for it. Problem is that it didn't come with the cable. I've found one and iwll probably order it ($9.99+ship) but was thinking of making one. Trouble is it's a 4 wire and I'm not sure if it's a straight through on all 4 or if any cross over at all and don't really wat to chance blowing it.
So if anyone has the cable and happens to know (or look) to see if it's a straight 1 to 1, 2 to 2, etc connection please let me know. I mess with electronics so have everything neede to make the cable, just don't know the wiring/pinning.