disassembling DT360 heat exchange system

[avianlaw]

I turned off both of the valves leading from engine into the interior of the bus. Also turned off the spigot valve next to the driver seat. cut off this section of the interior circulation and removed both heater exchange blowers and tubes. my question is: do I need to re-open the valves and connect them to re-circulate the coolant or can I keep them closed is there a separate circulation within the engine and radiator flowing?

I've also got a bucket of green antifreeze I don't know what to do with now.