+1 ^^^

I've got a Suntour wrench that fits the inside of the cup and the outside of the lockring of Suntour's old cartridge bottom brackets, looks a lot like the Park tool on the smaller end.

These cups were mostly intended for rapid factory installation, no doubt with an impact tool that probably looked like an old Suntour freewheel remover on steroids.
These consumer tools, made from formed steel sheet, might not really get a fixed cup as tight as one would want, but at least in this case the fixed cup is reverse-threaded, so no issues with the cup backing out and tightening itself against the inside of the driveside crankarm.
But, as I thought someone had mentioned in this or a similar thread, a piece of steel bar stock, possibly the blunt end of a large file, might allow further tightening of the fixed cup.

Item # HCW-11
Adjustable Cup Wrench
"The HCW-11 fits "slotted" bottom bracket adjusting cups and cups with "raised" 16mm wrench flats. These are common on older English bicycles, and less expensive bicycles. The opposite end has two ears that are 23mm wide and approximately 5mm wide."