Awesome progress and looking great!! You're blazing through the yuckiest part. A little late now, but a couple of cardboard boxes flattened out covers a lot of ground. A blanket works good when there's water involved. Lets the water through but catches the crap like a coffee filter. If you're fond of that cordless drill I'd buy a cheapo corded drill for the wire wheel. Drills don't like side load. Look for the RPM on the nameplate and get the fastest one you can find. A grinder actually works best but it's a little savage. NO LOOSE CLOTHING! You can also expect yourself as well as by-standers to be tattered with little poison darts
Safety glasses DEFINATELY required for anyone in the area. If you've got a shop-dog, put him in the back yard when the grinder comes out.
x3 on the manifold. I've seen cast welded with some sucsess (heat, weld, peen, heat, weld, peen, ...) but I've always brazed. I've also seen a lot of small block manifolds that don't wanna bolt up real good. Usually you can heat them (I've thrown one on the fire!) and use welding gloves while you get the bolts started.