Harman XXV top vent question

[Harman XXV 1986]

I just purchased a Harman XXV. I opted for the top vent kit, but the hole for the chimney is too low to use the 12" vertical pellet pipe that came with it. It will put me about 8" too high.

My question is: can I go from tht top vent kit straight to the 90° elbow? What precautions should I take, if any? Thank you!

Edit:
This is what I'd like to do

 

[Oregun]

One of the reasons for that short 12" pipe is make the outside pipe cooler so that when you open the top door to add more pellets it won't be too hot with the lid touching the pipe. Other than that seems like it should work ok. Be careful closing the lid so you don't burn your hand.
I think it runs 300 degrees.