Okey Dokey.... so where are we?   Oh yeah, plywood, 2x4 all that good stuff...   Okay, so the 1/4" plywood is cut to a 14" x 48" size and now we need to remember, the angle of the cut for the control panel area on the side panels was 10 degrees, so everything will need to be cut accordingly.   This is where a good tablesaw with adjustable blade angle is going to be necessary.
 
 

        So set the blade to 10 degrees and you'll need to cut the edge of the plywood so that it'll have a 10 degree edge on the front side and cut a piece of the 2"x4" to a length of 48" and then cut a small part of the top section all the way down length-wise at a 10 degree angle...
 
 

        Don't mind that small angle at the bottom of the 2x4, thats just a chunk missing from the wood, I will fill that in with some wood putty later to even things out properly.      Now you need to mark out the placement of the equipment that will go ontop of the plywood.    I measured out the Colecovision and added 1" extra for the width and 2" extra for the depth (cords and such in the back) and marked out where the pedestal would be for the Colecovision to sit ontop of.    Then measuring up 1" past where the 2x4 is going to sit underneath the front of the plywood I marked out for the joystick bases and for the fire buttons.