Let me explain the dilemma with respect to the corners:

The scans you have all seen (with the rounded corners) are with the camera placed at a slightly further distance than was used for the PG. The pros of doing this are: (1) the side and top/bottom borders are more straight, and (2) the focus is slightly sharper throughout the image. The cons are: (1) the cropped rounded corners.

It isn't possible for me to get a wider gate... the gate I am using was specially ordered, hand enlarged by Roger Evans for capturing scope films with the workprinter. When I mentioned the rounded corners to Roger, his response was simply, "move the camera closer". Thus the tradeoffs mentioned above.

The SW print used in PG was such that I was able to capture the entire frame without any cropping, and only a very minimal parallax that I worked around with the gradually curved border on the top/bottom. I experimented with removing the parallax in software (there is an avisynth filter for it - I think it's called "barrel filter"), but the results were awful and I never bothered posting examples.

I haven't decided if I will use the same approach with PSB, or if I will accept the round corner croppings that you have already seen. Maybe something halfway in between. Once I decide, I'll make a mask that preserves as close to every bit of the captured image as possible.