I'm not very keen on microcontroller hacking.
Which one would you
 recommend for something like this?  I'm guessing that for a fixed-speed
 job, you'd have the microcontroller, two MAX232 chips, and not much else. 
    Try something AVR (an Atmega 32 as an example) and BASCOM from
www.mcselec.com
    The code is very simple. Try to hack something and if you don't succeed,
drop me a personal mail, I cannot cope sometimes with the activity of this
list, although I love to read it.
    Greetz from Brazil
    Alexandre Souza
    
www.tabajara-labs.com.br