Re: CB350 Sly... Ton-less
The brake caliper behind the fork leg was a common modification when we roadraced the CB500's / 750's back in the day and it worked just fine.
The idea is to get the weight of the caliper behind the fork leg, to give a bit quicker steering (the aft location is what you see on most bikes today). The 350's caliper mount is pretty robust and doesn't give a hoot whether its in compression or tension, just like the bigger CB's didn't.
Another thing we did on the race bikes was to get rid of the adjustment screw and spring and let the caliper float - seemed to work fine on the track but I'd need them installed to get the safety check here in Ontario.
I'm doing the same change on my 175 tracker with the CB350 forks - reversed caliper. Still a bit of fab to do since I want the speedo (we talked about this awhile ago...).
Ages ago I had a CB350 front end on a 125 road racer with a second disc bolted to the hub using longer bolts (I had spec'ed out aircraft-grade hardware). The issue of course is how to hang on the second caliper. What we designed was a mechanical antidive that had a mount for the caliper and an adjustment so you could dial in some, a little or no dive or even make the front end climb if you wanted it to under braking. Looked okay on a race bike but I think the levers and arms and pivots might look a little odd on a street bike.
Let me know what you come up with regarding a larger disc - I didn't have any luck finding a larger 4 bolt rotor, though I guess I could get a carrier machined up. The CB350 caliper mounts aren't very amenable to adaptation for a larger rotor either but I guess with enough design, welding and machining, anything is possible.
Maybe the easiest thing for you to do is adapt a CB500/550 front end; a lot of the vintage road racers back here in Ontario do this and it allows you the opportunity to run twin discs and a lot stiffer fork to boot.
Regards,
Pat Cowan,
Pacomotorstuff