Now that is sweet. Post more photo's! How is the noise level burning down the street? If you want the link I have a briggs powered bike on here to check out.
Keep the boost bottle visible! Maybe under the tank but still visible. I always had people asking me if I was running nitros on my bike. It looks cool and that question will always crack ya up. Love the build man, ya got mad fab skills!
To switch out that carb I had to adjust the throttle cable. What you can do is measure out from the stop at the line going into the carb to where you need it and clip the cable to size and use some copper wire from any outlet plug wire and a bit of solder to fabricate a new stop on the cable...
Black leather straps. Dog collars with a cut open rubber hose from frame to tank for vibration - the taper of the tank may keep the straps moving. Looks tight. I would definitely find the right angle on mounting to keep that sweet look.
Yeah, I had one of thos Gyes saddles and it is the most comfortable seat I have ever had, well toe to toe with my brooks. You will love it. I had mine on a motorized and you really need something like that because bouncing around for a good part of a day will wreck you with the wrong seat...