[olddog]

First you need to heat cycle the engine several times and make sure that is the only leak.

Second you need to visually see the blocks crack. One to make sure it is cracked, and two to locate the crack.

If it is cracked on an outer jacket, here is how they used to fix them back in the day. Think Model A Ford. You locate the two ends of the crack. Go a 1/4" past the ends and drill a 1/4" hole on both ends. These prevent the crack from continuing to propagate. Now you tap the holes and screw a brass plug into them. Then you drill a hole next to the plug, but allow it to overlap into the previous plug. Tap and install the next plug. The next plug locks the previous plug into place. Repeat until the crack is completely filled with plugs. Adjust hole placement more or less to make the last plug come out in a reasonable spot.

All plugs must be tight enough not to leak, as they are all locked and not moveable when done. Then grind smooth. It makes a relatively strong fix, but a non-broken block would have been better.

I have heard of using this technique with steel, where you cannot get a deep penetration, then welding over the top. There are some very good glues that could be put over the top today.

Certainly not ideal for a race car, but you have nothing to loose but time if you want to try to save the block.

PS
use pipe plugs and pipe thread. This is so the threads taper and seal the water leak.