Installing headers -- While engine pulled or after re-installed?

Hello there. Years ago i put Hooker Super Competition fenderwell headers on a 65 Barracuda with power steering and 4 speed. . Engine in car in parking lot. Was not so hard as i thinking it was going to be. Took the afternoon to do it. No dinging anything. Currently have TTI,s for a 65 Barracuda auto with power steering. Soon as my back, 100% VA will allow i will get to it. I have new polylock engine mounts going in at same time. So i read with interest.