GL650 coolant capacity/changeout procedure

I want to change the coolant in the '83 GL650 I just bought because I have no idea when it was last done - but I'm not sure where the drain is or what the system capacity is, as well as any other procedures I should know about before starting. I'd also like to put in a new thermostat - just because the one in there may be 28 years old.



Any tips/advice would be appreciated!