Not using a resistor with 12 volt system is only acceptable if the coil is designed for 12 volts and would destroy the points in a short time.The only automotive coils supplied originally using points and no resistor may have been american motors(that I am aware of).
I think high idle vacuum about right, but why lower @ low idle?
Vacuum leak? spark retarded from port to dist closed?
When the manifold was refaced does it now cause the sealing rings to hold the manifold slightly off the gasket?
I think the leak is not massive but generally diluting the supplied idle mixture beyond the ability of the carb idle circuit to supply---small leak might NOT respond to things sprayed near it.
Maybe could pressure test manifold on engine by; plug threaded ports--remove pushrods on intake valves that are open--cover carb inlet with? hand?--apply air/smoke through threaded port--look/listen for issue ????--smoke from a cigar could be allowed in suspect areas to watch for draft
Someone else will give us some leak testing ideas.
