My main question is, why?
They are going to cost a lot more and be less functional off road with a smaller sidewall.
Some newer fullsize trucks look okay with 20s, but mostly because the trucks are bigger and the brakes are bigger as well. 20s and 33s on a Ranger will look retarded in my opinion. I have seen it but I don't remember where.
Having said that, 35s will rub if you actually wheel the truck. Although since you're looking at 20s I'm guessing that isn't a big issue. So my main argument is that is just plain isn't going to look good on that truck. I've seen a few Rangers with 17s and 33s that looked okay.
2006 F150 FX4 Super Crew - Bilstien 5100s leveled 2", 35" KM2s, 4.56 gears, Detroit locker, Eaton E-Locker, Traction Bars, AEM intake, Xcal 2
2010 VW Golf TDI 6MT