Steering box ID

I need to replace the steering gear box in my truck. I know that there are 32 spline and 33 spline boxes available and that they are identified by either a 64 or an 84 stamped into the casting.

My problem is I can't find any information anywhere telling me which one is which. Mine has a the 64 stamped and I would think that the smaller number would be the 32 spline but my common sense doesn't always line up with what the manufacture thinks.

I have honestly been searching everywhere I could think to find this info to no avail. Any help would be appreciated.