stick welding old thin header tubes?

I agree it's pretty dicey stick or mig on thinwall. I've had the best luck with gas, OxyAcetyl. I get waay better heat control and nice puddle/penetration. The key is to stitch it where you want it to stay, then go back and do short travels around the tube, 1st on one side and then the other. I put together a broken pipe that cracked off of a manifold flange,(flange on the pipe), just to get it to town. It ended being so nice it's still there and holding like new.