Wheel Cylinder Specs -http://chevy.oldcarmanualproject.com/chevyresto/4885.htm
NAPA had all the parts to rebuild the wheel cylinders on my 3800. I can not see it being any different for a 3100.
I would consider Copper-Nickel brake lines if you are going to replace them. A lot easier to bend and flare, and does not rust like steel. I wish I did it when I worked on my brakes. As typical, it is a more expensive and a little harder to find.
http://www.copperinfo.co.uk/alloys/copper-nickel/downloads/is49-cu-ni-brake-tubing.pdf Just taking a guess, you will also need new rubber hoses.
