I’ve been swapping emails with different people that are designing, or have designed and constructed various Z80 projects. In particular, Chris Jones of Poland. His web site is here. In particular, I ran across his post on successfully using the sd-reader library here. His post is one of a few that re-inspired me to investigate the sd-reader library.
Something Chris mentioned was the GODIL, which is a “modern day” Z80 hardware emulator. He writes “It was developed by some people on the BBC Micro forum at http://www.stardot.org.uk/ and also exists in versions supporting the 6502 and 6809. It supports the usual monitor-type commands, disassembly and so on, all while acting as a Z80 in your circuit.”
Many thanks to Chris.