that looks like it was MIG welded. MIG tends to throw slag which makes it look messy. Plus the pipe used to make those manifolds is thick walled cast steel. Most of the "hobby" MIG welders available don't have the power to weld pipe that thick, so you have to jack the heat up high and load the joint up to get some degree of penetration on the weld.
Those manifolds worked well when that car was running that turbo setup. Why do you insist on posting shit you know nothing about?