OK, I took those GOUT cropping examples from the speeder shot, and compared them to the video clip of that scene at the Senator. The green box is about how much was cropped in the Senator screening - it's only an estimate, as there were no "landmarks" at the bottom of the frame (just sand), and this isn't accounting for the curvature of the screen.

As you can see, there's either a little more or a little less at the bottom than the GOUT (not sure which), but a whole lot more is cropped off the sides. Here's one more example of the Senator cropping vs. the raw frame:

That is too much off the top, and WAY too much off the sides. As I related before, Mike Verta says this print had platter damage on the sides, so the projectionist had to crop closer to hide them. Also, my guess is that the Senator's screen was closer to the standard 70mm ratio of 2.20:1, so more would have come off the sides anyway.

However, that is probably far more cropping than you'd see in any normal theater in '77. You definitely don't want to crop off that much in your version.

Again, I return to my 0%-5%-10% diagram, which I derived from an SMPTE framing chart using the .839 x .700 aperture that, from what I can find, was the Panavision standard in '77. Here's the same frame above - the green box is 0% cropping, the blue box is 5%, the red box is 10%.

For your final cropping, try to stay near the blue box. Something around 5% will remove all the rounded edges and gate fuzz, but preserve as much of the usable image as possible.