Truck-oholic - they don't differentiate between the two.
The axle is already built and underneath my jeep and it was cut and narrowed to fit so I'm not looking to swap out or change the axle.
The Micro Lock is acceptable and maybe the best choice. The spot caliper looked like a good option because there wouldn't be to much fabrication to make it work. I just don't know if they are strong enough.
RustyC - Maybe I'm missing your point. That's what I think the spot caliper does, it bolts on the opposite side of the normal brake caliper, but it does grab the rotor when engaged.