Ok, so I finally got the '74 (or '75, don't remember which) modded Super Lead in. Took it out to my practice spot and fired it up for about 2 hours so far. It has a Kitchen Sink Mod to it (BE/HBE/C45 Pull Switch), an FX Loop added, a Saturation Switch, and a simple clean circuit that's foot switchable. We only messed around with the BE so far, as we really want to take the time to explore all the modes properly and dial them in versus trying all the modes for 20 minutes and moving on. So, all 2 hours spent exclusively on the BE.
We tried it with a variety of guitars - a Gibson LP Custom loaded with EMG's, a Gibson Flying V with
a 496R/500T set, and a Fender Strat with stock pups. I'm gonna bring out a Gibson LP Standard with Burstbuckers next time, just didn't have it with me today. We tried it through a '76 Marshall (Straight) 4X12 with 75hz G12M Blackbacks, and a late 90's Marshall 1960B 4X12 with 75's, and an '01 Mesa (Traditional Sized, Straight) 4X12 with well broken in V30's. We tried it straight in, as well as occasionally blending in a Maxon OD808 for different sounds.
First impressions - it definitely sounds the way a Marshall should. Very tight and percussive, responsive through all the guitar and cab combos, etc. Even with the BE being the lowest gain/saturation mode on the amp, we found it to have plenty of gain for everything from AC/DC and 70's rock on the lower end, through the 80's and Van Halen type sounds, all the way into old Alice in Chains "Facelift" sort of tones. You could roll the gain back to about "5" and approximate what the amp would have more sounded like in it's stock form. Using the same settings throughout, we back off the gain a little (to around "8") and started playing everything from old RUSH, AC/DC, Skynyrd, etc. Somewhere between 8-10 and we were playing Van Halen, AIC Facelift material, etc. Doing nothing more than kicking on the Maxon OD808 as a boost (using little to no gain on the pedal), we were able to easily get into old Bay Area Thrash range, playing with tones very similar to Kill 'Em All/Ride the Lightning, old Megadeth, Anthrax, etc.
We engaged the FX Loop and "Master" volume knob on the back and tried the "clean" circuit. I say it in that respect since it's not really a full clean channel, more of a cleaner signal. I told Dave I needed a clean signal to use live, didn't have to be a full clean circuit and he put this in for me which turned out great. Is it a sparkling Fender sound? No, nor did I expect it to be. It's a simple clean circuit to get me through live, which is exactly all I needed. It handled everything really well. Picking lighter on higher output pups (like the EMG's) can still elicit very usable clean sounds, where down to guitars like the Strat started sounded very much like full clean channel. I'm very pleased it, it turned out nicely and even it can get cleaner by picking lightly where making it break up for a little grit is easily achievable by using a little harder pick attack.
For the thrash and 80's metal stuff, we liked
the 1960B, 75 loaded cab the best. It just lends itself for that type of music. For just about everything else, the '76 G12M Blackback loaded cab sounded best (IMO) for everything from old rock, to Van Halen and AIC tones. It was tight, percussive, stop on a dime...but also very warm and smooth at the same time. The V30 cab had it's own flavor and a huge mid response. I think it would track exceptionally well on tape, probably more so than some of the others...but in the room we enjoyed the '76 cab more.
That's the first impressions, and of course it's only the BE mode. We still have to try the HBE, C45 on the modes, and the Saturation Switch.
More to follow, along with pics and video (just didn't have my cam with me today).
...let us know how you like each of the mods AND the sat switch 
I am happy for you. Soon you most likely will be Happy too. 
