I called John Parker today - checked a few things that he suggested. I've got it timed at 10 degrees BTDC with 35 degrees of total timing. This is in his range of OK.

35 degrees would be the absolute maximum. After you get the carbies sorted, try less. Ideally, get it set on a dyno.

I'd reduce your centrifugal timing to 20 degrees crankshaft & use 15 degrees static to get the 35 total, that lets you idle at the same speed with less throttle opening which then helps with your dieseling problem. I don't know what your cam specs are, but your compression is a bit on the high side for a small cam, so dieseling will always be a problem. Just put your foot on the brake, ride the clutch while you turn the ignition off & that will stop the dieseling. Down worry about the cam nut coming loose, I've got an auto that diesels for ages sometimes, it won't hurt so long as you torqued it up.