OK cut it with a sharp knife and a straight metal guide. That was easy enough.
I tried to glue it.....but I don't have much confidence in that working. It's a weird thing, nothing is straight on the back side so the glue barely touches the "wood" I am afraid....we'll see when it has dried.
Else I will go with Thorsten's solution, drill some small holes and use good old fashioned nails.
Something else...does anyone happen to have one of these coin door plates ?

I have come to the conclusion that I won't be able to use this coin-door after all. Although it really looks very much like the original one, there are some parts completely different on the inside as to where the coin guides and coin mechs go. Impossible to adept it all so I will have to fix up the original coin door now.
But gonna need another Midway coin door plate like that....don't think I'm going to get that one off nicely....