I assume you mean the '69 400/428 #46 heads. Several head ID sites list these at 68cc. From what I've read, most Pontiac heads actually measure more than the listed numbers.

http://ronspontiacpage.com/reference-pages/stockheadspecs.htm

http://www.classicpontiac.org/FAQ.asp?myPage=V8HeadInfo

http://www.bassettracing.cz28.com/custom3.html

The only #46 heads I can find, that came on 350's were in '73 & '74. Those are listed at 98 cc for most, and 89cc for the '74 GTO. Of course, I can't confirm any of these numbers. As we know, there is a LOT of incorrect info on most all Pontiac ID sites.