340 problems

For the popping and cutting out at 5000 RPM: Make sure no spark plug wires are touching each other (especially those that are next to one another on the distributor cap).

For the High idle issue start with the obvious: Is the idle adjustment screw set correctly? Is the throttle cable pulled too tight? Check idle circuits, float level…or rebuild it.

Also, that cam likes quite a bit of initial timing…and yes, even with everything working correctly, it will be a dog under 2000 RPM (just the way it is with that cam).