[Rich Biebel]

The last BB open chamber rectangular port head I am familiar with was the 188 casting. That was the last 3 numbers. It was found on crate LS-7's in the late 80's I'm guessing. They had 2.19-1.88 valves and one big difference from the previous 990 heads......hardened seat inserts( stellite) on the exhaust side. Peanut plugs as we called them were only on later heads. No production engine installed in a car or truck ever had those heads on them. GM Performance used to build special vehicles for display or use them for promotion. They also seemed to build some pre production stuff to see if there was interest.........Those heads have to be pretty old. My buddy has an original SS454 pickup and there is no way heads like that were on his truck when it was new.....he replaced the engine with a crate 502 a couple years ago.....