Huge congrats!
To find any documentation of the few chronographs JLC/LC featured during the 60's is hard.
Here is a couple of scans of the Grand Father of your E 2638.
Jaeger versions, 1945.
Love the case of this one!
But honestly, the two register is more of my speed...
LeCoultre version 1965.
LeCoultre versions 1969.
Best, my friend
Blomman