Honestly, I dont know the exact measure, but it does sit low in the hole. I know what youre getting at, both of you. 13:1 is ridiculous and if it sits low then it stands a chance of creating a lower compression regardless of the piston size. Let me know if im getting that wrong. Kev and I worked out some aspects of my build combing with this turbo. It WILL work out guys. He garuntees and warranties his work, ive got nothing but time to see this through. So we will take it step by step.
I was worried that I might be overdoing it Blair. But when i hit the woods with the 770 in LS with the guys, it was OK at best. I mean, it cooked and posted solid numbers but I still wanted some more. I really was on the fence with this decision for a good while before I hashed out the "GNCC turbo" kit with Kev. But since Team Rocket Factory is running a 798 in the GNCC with an 8mil crank and someone called Kev asking for 5 GNCC turbo builds.......I guess im not the only one whos crazy.
RPM, is what you are looking for...
a 770 build done right should Not be able to be ridden in the woods...it SHOULD scare you a bit, and not just be "ok"
ive seen multiple 770's post lower then 70 hp, even some in the low 60 hp range, not just because of a simple compression or deck height issue but because the combination of components was wrong or the build had one MAJOR flaw in a component choice or neglect of a necessary upgrade...it all reality a good running 770 on mild compression with a big head should be running in the 80's if all is done right with matched components...
dont give up on the 770 when the answer is right around the corner...
consider your options and the route youve gone with the current build...ask for advice from other sources then then ones previously followed, see what can be changed and what is truly holding u back... weigh the costs then the option to go turbo from there...
which ever u chose, good luck and happy motoring 
Balone...
4gunz, troywcc, and others rock 80+ Hp on trails all day long on 770 or larger builds and they are bulit very well.
Also, like you have stated before, some of the performance products used for duning/hillshoot are not always the best choice for a trail/gncc racer and will limit the HP that shows up on dynos (IE using a +3 TB vice a 54 or 58mm TB).
Last time I checked your riding ability determined how fast you can ride trails/GNCC, and no cam, TB, head, turbo, etc will improve, or deminish that. Chris can handle this rocket in any form or function he chooses, I've seen that first hand.
Bottom line, you can't buy skill, good thing Chris already has it.
Good luck with the build bro, in what ever form it may take. Hope to ride with you again soon.
Aaron
PS- anyone willing to go against the grain and push the limits of what we know, or what we thought we knew about performance options in this industry helps us all in the long run.
