I use the closed nuts along with the APE cylinder studs. I use new copper washers and spray them with a light coat of Permetex copper spray. For a street bike I would not use the open nuts on the outside studs
Unfortunately MTC doesn't make them anymore. The only cylinder studs I have ever used in my motors were the MTC Golden Studs. They are the exact dimensions of the stock studs but just made of a better metal. I also use copper washers on all 12 studs. If I reused some old ones I always annealed them and made sure they had a smooth surface where the head nuts came in contact with them. On the four outer washers I applied a thin coat of Three Bond TB-1211 on both sides of them. Never used anything but the stock head nuts. Never saw the need for those fancy cylinder head nuts!! Somebody in the late '80's did sell some Titanium copies of the stock head nuts. The price was crazy so I passed on buying them. I always follow the factory torque pattern in the shop manual and I never use more than 31 pounds of head torque. I never suffered any type of head gasket leaks or oil leaking from those outer studs.
1972 H2 750 Cafe Racer built in 1974.
1976 KH400 Production Road Racer.
1979 Kz1000 MK. II Old AMA/WERA Superbike.
1986 RG500G 2 stroke terror.
1986 GSXR750RG The one with the clutch that rattles!