To measure the chain line get the distance from the centre of the seat tube to the top of the chain ring, something like 45mm. The rear ends are 126mm, so half equals 63mm. The difference (63 - 45) will be about 18mm, which should be the distance from the centre of the rear cog to the inside of the fork end. Just do your own measurements. It was easier in the 1950's when the standard chain line was 1.5 inches.