Jerry McMillen’s posts on that thread were spot on.
Gear boxes are typically 2.1:1 reduction. So they require a different spec’d pump (1,750 rpm) than a typical belt drive (1,450 rpm). You could use a standard belt drive pump on a gear box, if you reduced the engine rpm. But that’s just silly. And likewise, if you had a gear reduction pump sitting around, you could find the right pulleys to install it as a belt drive.
1,750 rpm is still way better than the 3,600 rpm a direct drive turns, and it will have no problem pulling from a tank.