I'm about 90% done and have yet to attach the top, but here's my idea:
I was going to do the "Midway" method mentioned above, but since I used a piano-wire like system to attach (suspend) the monitor from the top, I'm thinking now to leave the back panel unconnected so I can use it as an "access" panel with the keyboard and floppy/cd drives attached to it. I'm thinking of attaching 1x2s to the top so that it fits nicely into the cabinet, and then using something like screen door locks(latches) and connecting by reaching in thru the coin-door in the front and thru the access panel mentioned above for the back. The weight of the monitor and wood guides should keep the top from moving, the latches are just there in case someone were to lift the table top. I don't think it would support the weight, but it should keep the top from coming off unless someone was trying to move it, which they shouldn't be doing!
Anyway, that's my 2 cents worth......