Looks like another great project! I went off to your website for your screen shots and thought to make a few observations.

I would recommend, if you are able to do it, to preview a snapshot of your captures to be sure you are not "crushing the blacks" or "blowing out the whites". Using Leia's slave-girl shot for my proof of concept, the screen shot looks fine until it is compared with the released movie (I'm using the 2006 DVD release; the 1983 release, as an extra on that same DVD, was darker and muddy).

Here's the 2006 DVD anamorphic frame (720x480):

It is fairly dark, but has strong color and proper highlights. A good shot. Interestingly, when your 16mm capture is resized for DVD anamorphic, it contains most of the original picture (bordered in green):

But when it is put in place, you can see it is way too bright:

Here's the problem -- you've blown out the whites on your capture. The grabbed frame in a paint program shows the spectrum has no darks and is off the top in whites -- too bright. I had to do some fancy settings to get it roughly down to where it should've been AND had reduced the color saturation slightly (because this process is error-prone and leaves the colors too strong):

Anyway, once resized and corrected, it looks pretty good over the DVD shot:

Here's how it would look with the DVD background removed. (Will you again do some fancy edging? At least, I expect you'll trim away edge garbage that I left in here for this proof of concept.) :

When viewed with the anamorphic flag stretching it to widescreen aspect ratio, it looks great:

Even when compared to the DVD:

Of course, if the capture settings are better to begin with, it won't need the kind of fixing I applied (with the inherent distortions in that process).