Super Zaxxon and Future Spy conversions from standard Zaxxon boardsets, so the flip screen hack is the same for all of them.]
On the top board (CPU) board, chip U55 74259 pin 11 is an output that drives the flip screen signal. In normal upright mode, this output signal is high.
To hack the board to force the screen to be flipped all the time first clip (or desolder and pull out), pin 11 of U55. Then follow the trace on the top side of the board, there should be a short trace about a 1/2 inch long connected to pin 11 that ends at a via. Attach a wire to that via, and attach the other end of that wire to GND.
Note, this hack will force the screen always to be flipped, so if you operate the board in cocktail mode it will not flip back for player 2.