Mate,
All you need to do is measure the hole and cut a piece of 12.5mm ply to fit. Or cut a piece of sheet metal 30mm larger than the hole and bend all the edges over 90 degrees, 15mm deep. Get a lock and measure how far down the hole needs to be for the tang to hit the metal stop, drill it and fit the lock. I've made loads for wedge heads and Williams games doing the above and never had a problem doing it. And every game needs a slightly different sized door. I don't know if they warp over the years, but no two are identical. So you are better off making a bespoke one anyway.