Actually the OHC was fairly popular considering. The OHC accounted for 21.4% of '67 sales, 17.3% of '68 sales and 24.0% of '69! Contrast that to what happened when the Chev six was offered - '70 saw only 6.4% of Firebirds with a Chev engine. That increased slightly to about 10% in the late seventies. Had the OHC still been available at the same time, I'll bet that the numbers would have been much higher, possibly close to 50% during the "gas shortage".
Who knows why Pontiac chose to drop the OHC instead of offering it in the Ventura body? Most likely reason was the cost to build them, but by then the tooling was paid for.
