First messages exchanged with a physical memory card. "Reset" (aka CMD0) puts the card in SPI mode. "Version" (aka CMD8) is the canonical method to check if the card is ok. The reply bytes come from the card and are the expected value (0x01).
A few hours later we can correctly initialise the card and detect the card type:
Update: And here's the root directory. It takes a bit of 32-bit arithmetic to locate it correctly. You can see the volume label in the first slot. It reads "GIGATRON".
Update 2: and here is a proper listing: