GM square ports

[Fast67VelleN2O]

I have seen many sets of single 840 and single 291 heads dated only 2 months apart as a pair. Many of these sets were on engines that were, from what I believe, untouched. Did they ever put one and one on engines?
Thanks
Matt

[JRSully]

I believe that there are documented cars that have one of each. The 69 Camaro ran into the 70 model year and some of the late 69 Camaros have 291's (a 70 model year sq. port closed chamber head) vs. the 840 (67-69 Sq. port closed chamber)