After looking through Vogons and another vintage computer site for hints around the PS/2 Model 30 Edge Card 3.5 Floppy Drives, I made a modified floppy cable so I could connect an IBM PS/2 Model 30 Edge Card (40 Pin) Floppy Drive to a (Modern in 1999) 34 pin Floppy connector inside a Dell Optiplex GX110.
The purpose is to read and write 720k Floppy disks and do repairs, tests and surgery on the other PS/2 Drives in a different computer without risking the PS/2 Model 30 itself.

Locate a 40 pin Edge Card connector (I found a pack of 5 on Amazon).

Locate a suitable ribbon cable to pull 6 wires from. Do NOT use larger wire, like in Dupont ribbon wire connectors.
I used a Molex 4 pin Disk Drive Cable - the Female end of a splitter - NOT a Berg Connector for 3.5 Drives.

This article has enough facts to make the cable. If you want more details you may want to study the Diagram from Github schlae PS2FloppyAdapter

PS2FloppyAdapter.pdf

h t t p s : / / github . com / schlae / PS2FloppyAdapter / blob / master / PS2FloppyAdapter . pdf
Delete the spaces in the line above to get the actual link.

Split out 6 wires from the Used Ribbon Cable.

Position the 40 pin Edge Card connector on the standard 34 pin Floppy Cable.
Where you put it on the cable relative to the Twist determines A: or B:
Be sure Pin 1 for the 40 pin Edge Card connector is at the right place in the Ribbon so Pin 1 matches, and think about where on the cable (front or back).
The ribbon cable should rest in the metal blade fangs that pierce the insulation (like a phone punch-down block).

Position the 6 wire ribbon at the 34th wire end of the ribbon so it fills the 40 pin Edge Card connector - thus providing wires 35 - 40.
Clamp/Crimp carefully in a vice, being careful to align everything properly. This took about 20 minutes to hold the cables still with careful attention.

You should continuity-check each pin - one probe on the 40 pin Edge Card connector - the other probe on a different connector on the cable on the same side of the Twist.
Verify each pin is connected.
Verify no adjacent pins are shorted.
Verify the 6 wire ribbon cable made a good connection to the 40 pin Edge Card connector and the end of the wires for 35, 36, 37, 38, 39, and 40.

On the 6 wire ribbon, the inner pair can be connected together (pin 35 and 36 on the 40 pin Edge Card connector). It's in the green shrink wrap.

Connect pin 37 (40 pin Edge Card connector) to a black or ground wire of the Molex 4 pin Disk Drive Cable Female end. Either black wire is fine.

Connect pin 38 (40 pin Edge Card connector) to the red wire of the Molex 4 pin Disk Drive Cable Female end. Provides 5 volts to power the IBM PS/2 Model 30 Floppy drive logic circuits.

Connect pin 39 (40 pin Edge Card connector) to the other black or ground wire of the Molex 4 pin Disk Drive Cable Female end.

Connect pin 40 (40 pin Edge Card connector) to the yellow wire of the Molex 4 pin Disk Drive Cable Female end. Provides 12 volts to power the IBM PS/2 Model 30 Floppy drive motor and control circuits.

Connect the 34 pin cable to the 'modern computer', power on, set the BIOS to 720k for the drive connector you're using.

Admire your handiwork and happily read and write 720k Floppy diskettes on the PS/2 Model 30 Floppy Drive 😀

Note that this cable already contained 34 pin Edge Card Connectors for A and B in the right places, and 3.5 floppy header connectors for A and B in the right places.
I added A and B drive 40 pin Edge Card connectors with a 6 wire ribbon cable parallel to the 34 pin ribbon.
A is near the end AFTER the Twist, B is in the middle BEFORE the Twist, same as a regular PC cable - NOT like the PS/2 Model 30 standard 40 pin floppy cable.

It is my intention to only use 2 Floppy drives at a time on this cable set.
With this structure I can use any combination of A and B drives - NOTE: use only ONE PS/2 Model 30 Edge Card floppy drive at a time.
I wouldn't power two PS/2 drives through the ribbon, it might be too much current.
If I use regular 5.25 or 3.5 drives on the 34 pin connector, they would be powered normally, NOT through this female power connector.

There are adapters to let you use a regular 34 pin drive in a PS/2 Model 30, I use these to add in Goteks when needed on that machine.
TexElec is one source, eBay has them too.

One Last thing, I added a 37 pin Submini-D connector on the end of the cable close to the single 34 pin header Controller connector.
This is so I could leverage the 37 pin external drive connector on the IBM Floppy Controller that comes in my 5150 PC's.