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Hi Andrew,
You seem to have more than one issue, based on the provided images.
First you should try to figure out why there is such a big difference in focus between the top and the bottom of the image. You seem to have some sort of tilt problem that can be caused by anything in the optical train, including collimation.
The devices that you mentioned can only guarantee collimation on the optical axis, which is good enough for visual use but say nothing about squareness of the focal plane to the optical axis. I'm afraid there are no easy methods for collimating a Newtonian astrograph. In fact that is the main reason I don't make such instruments.
The only thing I can suggest is that you take systematic test images where you rotate various components of the optical train and try to understand the tilt problem. Once you get symmetrical stars in the corners you can start work on tuning the camera spacing.
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