I actually purchased both the OEM Ford [made by VentShades] ones you see in the Ebay auction, and the common aftermarket VentShades you used to be able to find in almost any parts store. (I purchased mine from Green Sales, and they still have a few left.) Just as I suspected, the Ford ones were better. These are what I ended up installing on Lucille.
The OEM Ford VentShades are slightly different than the aftermarket versions. The aftermarket versions fit under the main window only. The Ford versions fit under the main window and have an extra attachment on the end that secures it to the vent window frame. This makes for a better, tighter fit. If you look closely, you can see it in the attached picture. I really like them, they are functional, and they look period-correct for these trucks.
Lucille: 1985 Ford F150 XLT Lariat
*Colors: Dark Canyon Red exterior, Canyon Red interior
*Engine: 5.0, CompCams 31-230-3, "Thumper" E7 heads, Edelbrock Performer intake, Autolite 4100 carburetor, DuraSpark II ignition, Thorley Tri-Y headers, Flowmaster dual exhaust, H-pipe.
*Drivetrain: AOD transmission, 3.55 gears, 2wd.