Well i got some time this weekend to play with both amps. I have found that #266 is a little brighter and more mid (bite) focused than #339. I decided to pull the chassis out and take a look at them side by side. Here is what i can see that is different between the two. First pic is #266. I am no amp tech so i posted these pics in a Bogner FB group and got this response...
Looks like #266 has the extra V1 board! Very cool! Those boards were on a small handful of the Rev2s and it changed up the mids, bass and gain, basically the input of the amp and how it reacted to the guitar from what I gather. Mine also has some extra board but it’s on turret board and all done by hand (more prototype) but also has a lot of wizardry done on V2, fairly similar to V1 that also reshaped the bass to be even more tight, and much more useable but still HUGE and 3D. There was a lot of experimenting going on back then on those early Überschalls, and sometimes you come across those Frankenstein Ubers. Very cool for sure! Those extra V1 board Ubers are pretty desirable!
It's cool both amps have their own thing going on, #266 is a bit more aggressive while #339 is chewy and deep. I picked up a quad set of '99 v30's and they match up great with the two greens. Can't wait to pick up a Morley ABC pro and run them together.