I have my fuel filler mounted on the fire wall even with the carb. I fashioned a mount using aluminum angle and drilled a hole in the cowl just large enough for the fuel filler to have the head flush with the cowl. This way al the lines are connected and don't have to be removed when taking off the cowl. Saito makes a couple of different nipples for their engines. I have a couple of the older muffler exhausts so was not a problem for the exit. You could also consider a flex pipe and mount the muffler so the exhaust points down.

I didn't use all the decals so not sure where the extra you have go.

JimO