These articles are about a prototype 5 liter Pontiac V8 from Repco. I don't have a copy of PEI's Autobiography, was he at Repco in 1969 and does he mention this?
https://forums.autosport.com/topic/110008-brabhampontiac-303-trans-am/
https://www.motortrend.com/features/ohc-pontiac-experimental-engine-found?slide=3
https://forums.autosport.com/topic/110008-brabhampontiac-303-trans-am/
https://www.motortrend.com/features/ohc-pontiac-experimental-engine-found?slide=3