Replacing my Intake Manifold Question

I am trying to drain my coolant before replacing my intake manifold. My 340 coolant plugs wont budge and I don’t want to brake them and have to pull the motor as it would be to tight to drill and tap under there.
So I drained from the lower radiator drain **** and also got the rear up as high as I can. Then I tried vacuuming out through the thermostat opening.
I don’t see any more coolant. I am wondering how much I left in there and if there is anything else I can do before yanking the manifold???
Thanks for your input!

IMG_1626.jpeg

IMG_1625.jpeg