Ding dang dong...I think the "heat stress" that I assumed resulted in the yellowing of the cucumber plants is really Mosaic virus. They look yellow and blasted (the leaves) and have a geometric pattern across them. Internet search indicates Mosaic virus, spread by aphids most likely (even though I have seen none).
And there are blooms all over the plants!
Does anyone have any experience with this? I suspect I need to pull the vines and burn them. With so many blooms on the vines, that sounds drastic. If anyone knows an alternative, I'm open to learning!
If not, well Boston Pickling cucumber either is not as suited for my area as my garden center wanted to promote, or I just need to try again in a different location or different time of year. (We're down here in Florida, y'all...)