Hi Doc!
yes, you can go back to the 6L6GC even after installing the bypass caps.
These mods are not related to each other. Matter of fact, the caps are the ones that provides some improvement that can be measured but probably not heard (or barely).
The (reportedly) audible or really sonic improvement is the tube xchange.
The ByCaps are installed facing the 4 big yellow caps on the opposite board. If it were already installed, it could be easily seen from outside.
Now, where exactly are mounted...is only for ARC to know and for us others to wonder... ;-)
I won't do the upgrade, at least for a while.
Maybe (just maybe) I'll try the tube, but not before I need new 6h30's (520 hours in abt 6 months..).
I've decided to enjoy what I have for what I bought it. Or else, the race is endless...and time is not.
brgds marcelo