Ive been doing maintenance and repairs on my own cars for 15 years and never once needed a torque wrench. I think their necessity is overstated unless you're building an engine that needs exact torque specs. But there's nothing wrong with being safe.

3/8" drive torque wrenches do exist: https://www.amazon.com/TEKTON-24330-8-Inch-ft-lb-13-6-108-5/dp/B00FMPKAD0

Ok, cool. I have this one from Amazon: http://smile.amazon.com/dp/B00FMPKAD0

Since it's rated for 80 ft-lbs, I should be ok for the 50 ft-lbs torque specified in the Curt install sheet.

This Tekton is in the range of what you're trying to torque to and will do most jobbies on a bike. A little bit of blue locktite on the caliper mounting bolts for added insurance if you're really concerned.