What's the best way to find a dead cylinder?

Put a vacuum gauge on it.. report back here with the manifold vacuum at idle, and observations of what the vacuum gauge needle is doing (steady, quivering, bouncing?)

Most likely it is something simple.. and it all needs to be checked before assuming the worst case...

A picture of all the plugs could help illuminate an issue... a compression test, checking the valve lash... if it has a mechanical cam and lifters..

Also where is the curb idle timing set at? Did this problem just crop up, or is it in part, why you rebuilt the carb?