Wow very good Knowledge but I would also do new valve seals just to be sure cause they might have been leaking also which would give him oil entering the combustion chamber through the intake valves, than mixed with fuel and air which will give you Grey smoke.
Wait lets think back in 3rd grade here. Black + White/Bluish equals what??? Mostly like grey
Black = Rich mixture taking place in the combustion process (Too Much Fuel)
White/Bluish = Process of burning oil taking place in the combustion process (Bad Rings, Bad Valve Seals, Blown Head Gasket)
I'm not saying all these things are bad on his motor but these are all possibilities but its more likely to be bad rings. Alright Blanco you get an A for the day, you may go home now. lol just messing with ya man.
Did you do a cylinder leakage test cause that would indicate bad rings and other things too cause a compression tester might not show that but than again it might.