Did WWII fighters have inverted airfoils for horizontal stabilizers?
From the Longitudinal Stability (Pitching) chapter in the FAA Pilot's Handbook, two things stand out to me:
One:

Regardless of the airfoil shape, nose-heavy airplanes like WWII fighters will almost always have downforce on the horizontal stabilizer.
Even if the airfoil is not inverted, it will be attached at a negative angle of attack.

Compensation for this nose heaviness is provided by setting the horizontal stabilizer at a slight negative angle of attack.

Cutaway drawings for the P-47 seem to suggest they're not inverted, example:
(Source)
Two:
Unless it's a T-tail, the propwash combined with the downwash results in downforce on the horizontal stabilizer.
(Source)

P.S. Do not rush to accept, wait for votes or wait for our resident aerodynamicists to answer.