generic approx 2x photo relay lenses
These typically have 23.2mm tube to fit microscopes and C-mount thread at their opposite end.
Similar 0.5x photo relays are used with a C-mount USB camera cube:
Since Nikon CF objectives are nominally free of chromatic aberrations,
truly generic photo relay camera adapters could work well.
Brooke Clarke compared a pair of generic camera adapters
which are no longer available from cited vendors Image Solutions and Optexcom.
A relay lens acquired 20 or so years ago looks similar to that Optexcom adapter:
Focussed about 5cm from C-mount thread to camera sensor,
that parfocal image is poor and distorted,
because it is actually intended for use with a C-mount camera sensor in very close proximity.
The Image Solutions adapter looks similar to currently-available AmScope CA-CAN-SLR-III.
Its Amazon price is higher than that for a used CF PL2.5X,
but includes a mechanical camera attachment that needs to be improvised or acquired for the CF PL2.5X.