Having light engine issues on mine and am replacing the light engine probably next week.
I looked at the service manual, at least the one I could find, and nothing about those screws. However on older models the screws to align the picture on the screen both up and down and side to side, are part of the housing or frame of the housing. The 65738 does not have those same screws. So it looks like, looks like mind you, these are the vertical and horizontal gross, for lack of a better term, adjustment to center the image and then you use the service mode to do the smaller adjustments.
At the same time as you noted not sure what it would adjust unless it rotates for vertical and slides the mirror and lens piece out for horizontal.
I can play with the bad one and see what effect is once I get the thing apart to do light engine swap.
E.B. White said, "I arise in the morning torn between a desire to improve the world and a desire to enjoy the world. This makes it hard to plan the day."