Please put a timing light on it and crank some initial timing into it.
Simple test, at idle, turn dist CCW and see if it picks up rpm. If it does the engine wants the timing. Everything that you wrote point to insufficient initial timing. Get it started, set timing to 18* and turn the idle down. If timing drops, add it back and lower the rpm. See where the idle ends up with 18* of timing. Most engines unless they are cammed crazy should idle in the 750-950 range.
