My 67 has a built 400 turbo trans. with 70-72 chevelle 12 bolt. The trans came out of a pickup, I am using slip yoke instead of bolt on yoke. What should the length be center to center on the driveshaft? Does anyone have this same setup?

If you just removed the bolt-on yoke and installed a slip yoke,you likely don't have much slip yoke travel.Check closely that the yoke position is centered and measure center to center at the u joints and have a driveshaft made.This bolt-0n yoke situation causes a lot of problems.If you use the bolt on yoke ,it has a 1350 u joint and your driveshaft guy can built a HD shaft to fit ...a little heavier and more expensive but troublefree.There is a modified slip yoke available special for this problem , but it still does not allow as much travel/spline contact as needed in some applications.
I will quote you a price on a built/balanced driveshaft if you do not have someone local . PM me.
Harold