Video select logic with Multiplex IC?

[SixteenThirtytwo]

I'm working on a circuit for my Atari ST computer which allows for
different monitors/TVs to be used, but I'm stuck when it comes to the
"logic" part of it although I think I have a functioning idea ;-)
http://img217.imageshack.us/img217/5754/atarimultiplexce4.png

Do I need a "multiplexer" type of IC as the "electronic switch" (U1)?
What about the "logic" ICs that control U1, setting it to 3 different
positions according to the logic state of the "mono detect" line and
the micro-switch inside the DIN-13 connector?