MIDI over long cable runs

[WeAreAs1 at aol.com]

Hello DIY'ers,

I find myself in need of a device that allow me to transmit MIDI data over
very long cable runs (a couple of hundred feet).  Past experience has shown me
that 30 to 40 feet is about the limit for reliable MIDI communication, using
standard MIDI hardware.  There are a couple of companies who make and sell
boxes which will send/recieve MIDI over long cables (J.L. Cooper is one of
them), but I would much rather build my own, if at all possible.  Has anyone
on the list ever made such a box?  

I was thinking that it might be possible to use some of those RS232 interface
driver/reciever chips, such as the MC1488 and MC1489.  The level-shifted
differential signal would be sent down a standard XLR microphone cable.  Does
this sound feasable?  Are those chips fast enough for reliable MIDI data
transfer?  What voltage level would you recommend that I use for the driver
signal?  Are there other interface chips which I should consider using?  

The MIDI signals will be originating from the keyboard of a modern MIDI'd pipe
organ, mainly just to let the organist play the occasional piano or bell/chime
sound from a MIDI module, so the cable and interface won't have to deal with
any high-bandwidth data such as sysex or multi-channel sequencer data.

Thanks for any ideas,

Michael Bacich