My 42 has serial number 101 on frame and different style stamp 101 on barrel. Obliviously non factory. They seem to match very well as far as wear. Can it be ballparked how early my barrel is?  Its 3″ and was told “most early 42s were 2.5.”  My research found 3′ was first in the 42s with 2.5 coming in 1935. Is this accurate? More experienced thought on this would be appreciated.    Thanks Dennis