If we're getting into details:
- do outside.
- clamp the manifold down with a couple of big "C" clamps to something solid. I used an outside workbench and kept the exhaust port about 8 inches from the bench top edge.
- you don't need to heat the entire manifold, about 2 to 3 inches around the stud should get cherry red.
- let it cool where it is.
- have a fire extinguisher and a bucket of water handy, but DO NOT use the water to cool the manifold. The water is for you. If you get burnt, get the burn wet, and keep it wet.
- wear welding gloves, welding goggles, long pants, shoes.
- be careful (that goes without saying)
I've done over a dozen small block sets in this method.
Jim