looks like a Winbond clone, but by whom?

A real winbond for reference

Yes, looks like Winbond, a ubiquitous Hercules clone.

One of the jumpers selects the external character generator ROM, the other disables the LPT.

I'll need to make a DE9 to DIN6 cable now...

The wires you see on the first photo were connected to an external switch to select between the character ROMs.

Good to know that the LPT could be disabled: I already have one on my multi-io card. Is it closed disabled or open disable, do you know?

Badscrew wrote on 2021-09-18, 11:31:

Good to know that the LPT could be disabled: I already have one on my multi-io card.

Remember that the parallel port on MDA/Hercules cards is at port 3BC, and thus won't conflict with a parallel port on a multi-I/O card at 378. You might still want to disable the video card parallel port to avoid the multi I/O port becoming LPT2.

with two parallel ports you could do a stereo 8bit R2R DAC !

Badscrew wrote on 2021-09-18, 11:31:

Good to know that the LPT could be disabled: I already have one on my multi-io card. Is it closed disabled or open disable, do you know?

In the card I have, closed = disabled.
But indeed, it probably won't conflict with the I/O card.