Is the Gap Between the Window Header and the Header a Problem?
If it hasn't been a problem in the past, it won't be in the future. 50 years is a pretty good test.

I am also pretty sure that when the home was built the header was tight, but shrank when everything dried out over time. It happens in every wood framed house.

If you choose to, you can add a shim in the middle or in two places and snug it up in place, but that would at the most. I would think that the sheathing on the outside is helping to hold everything up, which in reality, isn't a whole lot of weight over that window as long as there is no snow load.

I would think the rafters are situated so that they are near the ends of the beam, not in the center so that minimized the use of the header.