Congratulations.
I thought about putting a wider control panel on my MK Mame cab as well, but was worried about it being too wide for the players to stand in front of the monitor. Guess I have my answer now.
Not sure that was a dedicated MK though, looks more like a MK II to me. It doesn't have the same angles under the control panel as a MK I.
For reference, here's a MK II:
http://www.klov.com/game_detail.php?game_id=8756I think this is your cab. They are practically identical to MK I's aside from that small cosmetic difference.
To mount my PC monitor inside, I cut out a piece of plywood as wide as the interior of the cab and sat the monitor on it as a shelf, making sure the angle was the same as the old monitor, which actually turned out to be pretty steep.