My apologies Boston14, what you said previously is perfectly clear. I've been staring at this screen too long and are loosing the plot!!
Read Martys post upside down - early is smooth and later is ribbed.
Does anyone have a engine bay pic of a 69 bb with ps, a/c and smog?
Is that the smog pump under the alternator in Paceme's 69 pic above?
If that's so, then the single groove for bb would have found usage on 67's [different emissions standard] and 69's [different component arrangement], but as best as I can tell, not 68's, not even exports with AIR delete [if mine is anything to go by]