"JJD, I see that AC 43-13-2B Fig 8-4 and FAA-H-8083-13A (Glider Flying Handbook) fig 12-4 both show photographs of Schweizer hitches installed inverted. Would this constitute approval?"

Fig 8-4 does show it upside down.... on a tricycle gear aircraft.
For all taildragers it indicates the hitch to be upright.
So I would not consider a installation to be compliant with 43.13 if installed inverted on a Pawnee.
In my opinion, 43.13 would not be acceptable or approved data for the inverted install of a hith on a Pawnee.

The glider flying handbook would not be good data for making any modifications to a Pawnee.

I agree 100 % that 43.13 can be approved data for a major repair or alteration. But.. it must fit the situation in question.
So if you've converted your Pawnee to a trike, all is well.
If not, you are noncompliant with 43.13.