I've read a few tapes purportedly from the Zilog S8000 using a DEI drive, and a quick look at the data captures in the Saleae GUI appears to show an MFM format, but with the data block anatomy unknown at this time.
So that I can orient myself to the data pulses I see in these captures, I'm reviewing the
DEI (Data Electronics Incorporated) Series CMTD-3400S2 6400 BPI High Density Cartridge Magnetic Tape Drive Operation and Maintenance Manual
It is believed that this is the drive that these tapes were written with.
Here's what the beginning of the first block looks like: