Corrosion in recessed spark plug receptacle from dripping antifreeze

I have a ford pickup truck with a v-8 engine the spark plugs set down approx. 3 inches below the throttle body and head both aluminum alloy and the block is steel the right rear plug has a heater hose connection above it and has been slowly leaking antifreeze for what appears to be some time. I have tried everything suggested to remove the corrosion including baking soda and water solution, muriatic acid wash, soaking with WD-40 over night, and trying to warm the engine prior to removing the plug my problem is, there is so much corrosion around the plug I can't get the socket to seat itself on the plug. I also have limited access and no view of the corrosion other than what I have been able to scrape out with a small screwdriver and the corrosion is gray. Any suggestions for me I'm going to try phosphoric acid next but still not sure it will work .