I took a clearer photo on my 95, if that's where the leak is coming from that's your rear heater control valve. AC Delco catalog shows one version for conversion vans and another version for factory auxiliary heat.
1995 Emerald Green Chevy G20 350TBI Gladiator conversion
Not sure if it would help but on mine the coolant only flows to the rear heater in heat mode so you might be able to get away with just using the front heater in vent or defrost mode to prevent it from leaking until you get the chance to fix it.
1995 Emerald Green Chevy G20 350TBI Gladiator conversion
It must be because of where the leak is on the rear valve, and by having heat on the coolant flows right to the back instead of being pressurized against the valve and leaking.
1995 Emerald Green Chevy G20 350TBI Gladiator conversion