Yes, again just my opinion and I'm not really in the loop with the latest price guides and auction results for pace cars but I believe a real, original docs, numbers matching big block, non A/C, Z/11 (especially a 4 spd car) is worth 10K more than an equivalent small block pace with A/C. I think that is a fair number.
Without giving away the location of the cars you are looking at do you have any more info or photos that you can share as far as condition and options
to compare with?
I don't disagree with the worth of a BB in comparison to an A/C equipped SB Z-11, but I would make dang sure it was an original BB car before I turned down a SB w/ A/C in deference to a made-up BB. Too many transplants around to try and make more money from the unsuspecting and/or enthusiastic buyer. I like the ability to roll up the windows and cruise in comfort (especially since my age has crept up on me).