possible bad head gasket

I have an 84 VF700F with 48000 miles on it. The issues that make me think there is a bad gasket are if I keep any coolant in the reserve bottle it will start hard and puff white smoke. The bike will run and start fine if the bottle is left empty or near empty. There are also air bubbles coming from the return tube into the reserve bottle. Other than a leak down test is there any other way of determining which set of cylinders are leaking, maybe if I remove one set of plugs and turn it over and check the bottle for bubble I will determine the bad set of cylinders.
I just changed the coolant and it was crystal clean, no oily films and there is no white foam on the dipstick or fill cap so the leak must not be major.
Any advice besides selling or parting out would be great.
Thanks

 

Check the oil for "chocolate milk shake"

 

Nope, dipstick/oil fill cap are are clean. When I changed oil last fall for winter storage the oil was not foamy nor discolored. Just normal used oil.

 

Maybe try a pressure test on cooling system first.

 

your plugs will tell you which cylinder has the leak. plug will be white

 

I know the cooling system was leaking. The O-rings were bad on the chrome coolant pipe coming from the water pump. I replaced those, changed coolant and that's when I noticed the air bubbles in the overflow bottle, maybe it was just working the air out of the system.