Danny Russell designed the Naylor Superdrive 60. Joe Naylor owned the shop/company in Detroit at that time. After about 3 years, Joe decided to sell Naylor Engineering to Kyle Kurtz. Kyle enlisted Dave Friedman to develop the clean channel for the Duel series. This was around 1996. Guy Hedrick designed the reverb circuit for the Electraverb series.
Billy Howerdell went to Dave Friedman and had him mod his '78 or '79 JMP with the Superdrive 60 preamp and a clean channel which was pretty much what the Dual 60 was at the time. The difference is mainly the power section is a Marshall JMP power section running EL34's.
I've had about 10 Superdrive 60's, a Duel 100 (made by Dave King) and I had Friedman do the APC Mod (Naked) to a '79 JMP 2203. I've owned that Electraverb 60 Tri-Tone custom that has been sitting on Reverb for about 10 years now as well. I also owned one of the first 20 Superdrive 60's.
The Naked is geared more toward lower tuning stuff, like where Billy tunes to for APC. It sounds good in that realm, but it didn't sound great with stuff tuned up higher. The Dual 100 was a nice amp. The cleans were pretty much the same as the Naked, but the dirty channel was the smoother Naylor tone. The Superdrive 60 or Superdrive 100 is where it would be at for me.
There is one main difference in the very early ones and everything from then on: The first ones didn't have the stacked gain pot for the dual-stage gain control. To me, they didn't quite sound as full, but the tone was the same and all. The stacked gain thing added a tad bit of fullness to the amp, and I can hear it on all of the newer ones that have it.
Dave King is a great guy, and I wouldn't hesitate ordering from him. I plan to order 2 within the next year. I hope this helps answer any of your questions.