it might be possible to use an 8-way jopystick but you'd have to keep the following in mind...
-I believe the 49-way joystick is a digital stick, and uses a chip to compress the joystick data, that would mean that you would need that compression chip to use any stick with the game. [As 2/4/8-way sticks that use microswitches are analog]
-The gameboard may connect the sticks directly to the board through a custom harness [not sure never seen a GL board before]
-If the game uses a 49-way stick it is obviously for good reason, so an 8-way could greatly effect gameplay.