It's definitely not a WD1001-type interface, as the usual TRS-80 early hard disks were. On that interface pins 43-50 were all +5.
It's clearly a SASI interface, which had been around since 1979.
SA1000 controller document. Look at the bottom of the board; you can clearly see the 8 data lines at pins 2,4,6,8,10,12,14 and then, sneaking around the outside, the parity bit at pin 16, then a lot of nothing, then the usual status and handshaking bits at the high end of the connector.
I've got a similar early board from Ampex for the IBM PC. Just a bunch of SSI TTL, nothing more. I suspect that you might even be able to rig up a SASI interface using nothing more than a bidirectional PC printer port.
FWIW, this also fits in with the only other PCP card that I'm aware of--a floppy controller for the Model III.