I'm still using the original "C" code 1982 heads on my 82 Suburban. They're very visibly cracked between every valve seat but it has never caused a problem. I did install copper tubings where the water passes through just in case. What I like about these heads is they deliver very good fuel economy.
1990 ¾ ton 4x4 Chevy Suburban
-Cummins Diesel - 12 valve - factory rebuilt
-6 speed bullet proof manual transmission - NV5600
-Gear Vendors Overdrive
-Upgraded Holset HX-35 turbo
-NP205 iron transfer case
-3.73 gears
1982 ½ ton Chevy Suburban
-6.2L diesel - high nickle crack free 1982 block
-Stans headers
-Ported heads
-Timing gear
-4 speed automatic
-3.08 gears
-30 mpg on freeway