I have a size 42 (1940 Pattern) which is currently in shipment from Norway to Australia which I can measure for you when I see it again.
Otherwise FWIW if you are looking at getting one, I wear a size 40 dress shirt and suit jacket and the ELC size 42 for me means I have room for a jumper underneath but at the same time I can wear it with just a shirt without being swamped in the thing.
My opinion is for anyone purchasing an ELC Irvin, get the next size up (2'') from your usual dress jacket size. Also be aware that if you are tall you will need extra length. Being 6' 1'' I had an extra inch and a half added to the body and arms which was perfect, but be aware this is more than ELC's usual extra 1 inch for long sizings.