Ok, this is odd - I had originally copied this from my Windows machine to the SD card, I just did it from my Mac with the exact same file and it's now working... No idea why, I didn't reformat the card or anything. Thanks so much for the quick responses, I appreciate iot.
I just received my El Cheapo from K-Retro, if I boot off of the Benn Venn boot.bin, it loads and shows the firmware as .08 - if I copy the boot.bin from the v20240409-a.zip file it will not boot and just says no boot file.