GMC SAFARI coolant line help..

I have an aging 1992 GMC safari.. extended van..

i use this as a cargo van mostly, and have no need for the AC in the back or
the rear heater..

the AC is already pooched but the rear heater (driverside middle) is
starting to leak coolant from the rotton plumbing...

does anyone know how this system works.. because i want to bypass those
lines as close to the motor as possible... there is a feed and return line
that comes from somewhere on the passenger side of the motor.. and it may be
actuated by a vacuum valve.. does anyone have a diagram, or has anyone done
this before?

thanks guys