You show the inside of two different case backs - neither is correct for your watch case. The straight lug should probably be a 105.003. Do you have both of them? Or is one to show what you think it should be?
I also note the “OXG” on the movement - this was placed on uncased movements imported into the US to be assembled there (to save duty). See this thread:
It is my understanding this was generally done for movements to be placed in gold watches manufactured in the US. So, a couple of theories here:
1. The movement was originally in a gold, US-cased Seamaster chronograph (this is where you see these movements a lot), then later put into a Speedmaster case (with an incorrect caseback).
2. It was cased into a Speedmaster case with the incorrect caseback in the US originally.
I lean more toward 1, that this is a put together pieces and that the movement was never intended for a Speedmaster. Also, the chronograph seconds hand is not correct for an Ed White, so indicates some cobbling of incorrect pieces at a later date already.
