I managed to source a replacement throttle shaft from member dogbunny and it arrived yesterday. I am very lucky there are people around like him or I would have been screwed. I put the carb back together, set the float heights and tested for fuel leaks off the bike.
The carbs were set as stock - needle on 4th ring, fuel mixture 3/4 turn out, original jet sizes. I have the Heiden tuning replica original mufflers (exhausts).
The bike started on the second kick, idles perfectly, no backfires, no fuel leaks.
I'm still thinking it has to be too good to be true. I have a couple of cosmetic things left to do before I put the bike back together and ride it but it's looking good.