Sorry missed these posts
I believe it's a cap change in the input and then its running a 12AT7 to reduce the gain and then I hand selected the power valve that stayed cleanest for longest.
In terms of using it on guitar I have tried it and it sounds great, very clean, clear and full, I would suggest if you want it for guitar that you swap the pre valve back to a 12AX7, but nothing has been taken away from the high end, just added to the low end if you get me.