[deuce_roadster]

Once bolted to a block it might be difficult to get in the right position to weld with a TIG or MIG. I like the idea of bolting it to an exhaust manifold for more room. A lot will depend on how good a welder you are. That is relatively thin and it looks like an old weld is there so you will be welding something thinner to something thicker. Do you have a lot of experience? I generally use my TIG on clean and well fit up new metal.
IF it was mine I would blast the inside and outside to remove rust and old carbon first, otherwise you will have contamination, then lightly grind with roll lock disk the old weld.
Welding is all about the puddle, and getting in a comfortable position. Good luck.