Also agree with Terry's magnafluxed test.
The water bit on a hot block could be questionable; but most probably the fire did not hurt anything for this reason:
Have a 1920's welding manual showing how to properly weld vintage cast iron engine blocks without causing multiple cast iron stress cracks as follows:
1. Place block on ground & line perimeter around block with bricks about 18" high.
2. Remove block & build a roaring fire with "lots" of wood stacked up within the brick wall perimeter, & keep adding wood until the enclosure is full of burning embers.
3. With a shovel, make a recess in the embers & set block on embers, & cover block with burning embers, & cover embers with galvanized roofing.
4. When hot, remove block, weld block with acetylene torch, & place block back covered with embers & covered with metal roofing.
5. Allow block to cool until embers burn out.
Naturally, this was the same 1920's generation that baked bread at home & killed & plucked their own chickens.
No doubt the bread was good, the corn fed chickens were better than chickens today -- my guess from stories that I heard from vintage welders is that the weld also lasted -- in 2013, if one makes bread once, allows time for dough to rise, & then bake -- with this much time consuming work, the next loaf will most probably come from the store -- at least the block was not discarded.