motors on which end of screw

[Jonathan]

float back n forth effectively causing backlash

Just in case Dean reads up on this it's generally referred to as end float, and often mistaken for backlash.

Knowing the machine you intend to build I think you'll find it's not designed to take 2 angular contact bearings like I describe but a single STD bearing

STD bearing, is that 'STanDard' bearing? If it's the one of the two screws I think it is then it's one of two cases. Either thrust bearing and standard bearing, or a double row angular contact bearing or pair of thrust bearings.