Hey there Hoss.
When you rebuilt the carb, I'm suspecting you found it pretty nasty inside with residue from long gone stale fuel.
When you rebuilt the carb, did you ensure all the fuel circuits in the carb body itself were clean and clear? Often times these circuits, particularly the pilot, idle air, and choke circuits are very difficult to get cleared out, especially the pilot fuel circuit. Any hope of restoring the carb to good working order usually relies on a carb soak solution and/or ultrasonic cleaning for several hours.
If that's all good to go, have you tried making adjustments to the idle mixture and speed?
If after making adjustments you still have a lean/high idle condition, you likely have an air leak. Being that you replaced the top end gaskets and reeds that should eliminate any sources of leaks from the top end. Your next suspect would be the crank seals. Being that it sat for a long time it is very possible your crank seals have lost their flexibility and sealing properties. Do ensure you don't have fuel delivery issues before tearing in to replace the crank seals though as it's a bit more of an involved job.
And yes, your leak down tester will help you zero in on if there is an air leak and where it is. You can somewhat cheat a little, remove your stator cover, start the engine and spray a few snorts of fuel mix from a Windex bottle behind the flywheel. If there is an air leak at the flywheel side crank seal, you should see the idle speed go down. Clutch side seal you really can't conduct that test unfortunately as the crank seal is not accessible with the engine in a starting/running state.
Good luck
