To avoid the work done designing my SD interface being wasted I decided to verify the concept before going any further.
I used my Bus Pirate to verify that the SD card I have would respond to the commands I expected using the protocol I expected.
The Bus Pirate supports many bus protocols including the SPI bus that the SD card supports in the mode I'm using.
I don't have an SD card breakout board so I ended up buying a micro SD card with a standard SD adapter and soldering some right angle pin headers to the pads. This gave me an SD adapter that would plug into a breadboard.
I initially used the Bus Pirate's probe cable as a quick way to connect to this adapter, but this got frustrating as the mini grabbers had a habit of letting go at inconvenient times. To get around this I made a quick adapter on some stripboard.
This little adapter also makes it easy to remove the SD adapter from the Bus Pirate without having to look up the pinout again. It should come in handy on future SD card related projects and maybe for writing raw data to the SD card.
Unfortunately I don't have any logs of the session, but with this adapter and the Bus Pirate I was able to initialise the SD card and read blocks of data. This gave me confidence that my project would work and would be worthwhile.