Nope that frame is a completely new fabrication...first of all the dimensions are way different than a stock SL which comes originally with a 14" rear wheel. It's a beautiful job, if you saw them next to each other you'd see how different they are.
I lengthened the swingarm by cutting two swingarms...then I cover the junction with a tube to strengthen it.
For the first five years or so we ran a custom frame I built for the bike. But I rode it once and cracked the frame (it weighed 7 lbs). I felt there were to many compromises with the design and I didn't want to build a new one so I modified an SL70 frame. Few pounds heavier now but much "tighter" feeling on the track. Lots of details on the building of the bike here:
http://www.jrbranson.com/HondaRacer/mainpage2.htm
Although it hasn't been updated in a while and much of the information is out of date.
Jag, do a search on "Takegawa" should bring up lots of speed parts for the Honda 70's. The 4V DOHC head is about $2500 ...so it would be an expensive experiment to see if it would fit. Can't find the link for the supercharge right now....there was a guy in Arizona selling them. Also numerous people have made their own. As of now there is no big company making them. They run about $1500.
I don't know why no one else in the USCRA is running one of these engines, they go like stink if you dump about $1500 into them. Race cylinder head about $300, carb/intake $100, race clutch $400, close ratio gears (1st and 4th) $100, Mag/CDI $300, pipe $150, alloy cylinder $100, race crank $150. Prices have come down a lot since we built Mary's...probably have $3k into the engine.
JohnnyB