Ok, so I think I *may* have solved at least this issue.
What worked for me:
1) Using `cat` to merge the MBR, the data-after-the-MBR, and the actual sda1.dd.img file into a single .IMG file on another drive. Running `hdiutil pmap` on that image showed that it was recognized as a “PC Partition Scheme.”
2) Then running `hdiutil attach -nomount` which attached the “FDisk_partition_scheme” and “DOS_FAT_16” partitions.
3) Running `mount -o ro -t msdos` to manually create a mount point. This gave…