While I have no idea how to put hardware together, I’ve been putting more thought into standardized Pi hardware that can be used as a development platform. For the Piboy advance, I’ve made the following drawing of the resolution and inputs. Specifically the hardware uses a 3.5 inch 480×320 inch screen, with a dpad, right and left buttons, four face buttons and two buttons for start / select. Though in practice, these would be better labeled as “Pause” and “Home”.

Not pictured is the on and off button, (which would probably be under the left hand side of the device), or the volume slider (which would probably be on the right hand side of the device). And video out and power in, would be placed on the top of the device, so it could be charged while be used, and the output could be sent to a larger screen.