O2 extentions and header bolts

[mgbrv8]

I am making a set of O2 sensor extensions for my 91, is there a length I should not exceed or a optimum gauge wire I should use, I will make them equal length no matter what? Now I am also using stainless allen bolts on my stainless headers with stainless lock washers. Should I use the factory torque or should I go a touch more due to stainless being softer and possibility of stretch?

Dave