Nice ideas. I'd wondered about the 'washer trick' myself in the past - that'd probably be the first thing I'd try as it should be realtively easy; if the throttle stops weren't seized onto the shafts of the carbs that I have, it's be a ten minute job to try it. Anything that reduces the air leak will help, after all.
Hadn't thought of peening. As I said in my other post, the metal on these carbs seem to be pretty soft, so there's a good chance that would be possible.
O-ring - not sure there. I bet the holes wear oval due to the forces on them, so maybe that would either be too tight or not seal nicely.
Ha ha! :-)
cheers
Jules