I know I read a thread on this creeper gear contraption, and I've been trying to find it, but no joy.
It was either long ago when we lost some old threads from this forum, or from another forum, or maybe I dreamed the whole thing. (entirely possible as old age encroaches)
Any way, I seem to remember that the 3pt hitch does not (cannot?) function with the creeper gear installed.
All the hydraulic output for the 3pt is re-routed to provide lubrication for the shafts/bearings/gears in the creeper gearbox, which is too high above the transmission to get any splash lube from the transmission.
I also remember that running the tractor with the creeper installed without the hydraulics to the creeper hooked up will quickly lunch out the creeper gearbox from lack of lube.
I have no evidence to back any of this up, so don't quote me on this.
YMMV.
Any similarities between this narrative and actual reality are strictly coincidental.
That's my story and I'm sticking to it.