Good question. I'll take my shot; then others can shoot at me -
Out of all the 1969 production Camaros, roughly 18% were equipped with C60 air conditioning. You can bet the percentage of convertibles w/ A/C was a lot lower, maybe 10% ? Less ? Good time for the numbers gurus in residence -
6.5% of total production (15,866) were V-8 convertibles. Of that number, 23% (3675) were Pace Cars. If you assume (I don't like the word, but there it is) 10% of Pacers were A/C cars, you would get about 367 total. How many big blocks ? roughly 200-300 from what I have read - if you apply the same formula to big 'uns as little 'uns, you'd get about 20-30. Rule out the 375 horse cars from the mix, cause solid lifter cars could not be A/C equipped by rule. My estimation - a lot lower number than that on both sides of displacement combinations. Probably saw very few in the northern climes, more in the south and southwest (which is one of the reasons I believe my Z11 was fortunate). I have seen a couple that had dealer-added underdash air, but it's uncertain at what point people added them. On a local level, of the three Pacers that were owned in this area, two had A/C, one did not. All three are small blocks.
This is conjecture on my part. I would have rather you asked how many had the ZL2 hood (lol) - we know that percentage !
Other opinions ?