It was a dish piston Dave, don't know the exact compression ratio, probably around 9-9.4:1 like most reds from that era. It was a rebuilt red 202 40 thou over with Yella Terra head and 30/70 cam, extractors and standard 202 inlet and Stromberg with HEI dizzy. The bigger cam than standard may have helped it not ping, plus the dizzy would have ben from a lower compression blue motor so the spark curve may have helped. The engine used to run a 390 4BBL Holley in my Torana but when I took it out for the 1980 WB I made it look all proper pollution-like to pass rego. The WB was a VK EFI trimatic too which may have helped it not ping as it used to change down pretty well in the tonner, seemed happy with the vacuum source signal and the electric knockdown seemed setup right.
E10 is normally around 94-95, very close in RON to 95 ULP. When I got my Cross8 tuned (and exhaust) it could no longer run on normal ULP as it was tuned for 95 or E10, ran happily on either.