You don't need a metal plate, but you do need something on top of the stick. Check out Oscar's diagram on
Mounting Happ Galaga/Pac 4-way in Wood Panel If you have some Plexi/Lexan on top you should be fine. If you plan on putting the CP overlay under the plexi/lexan then you'll probably need to put a thin plate over the top though (to cover the indent)
I used this way of mounting on my Galaga standalone CP and it works great. I can say you don't need the metal plate for strength anyway.
If you want the dustcover under the top panel then you need to make sure there is enoug room for it. In my stick at least, the e-ring on top of the stick lifts up the dustcover from time to time and it would get stuck under the top panel. I just took out the dust cover, but you could also route out a bit of space for the dustcover to lift slightly. I wonder how the metal mounting plate handles this problem.