It's May, it's time to be skiing not wrenching. I'd say give the JB a shot and hit the water. Watch the engine, keep an eye on the repair, and plan on fixing it correctly come October. Of course, if it's holding fine and there aren't any issues, push it back to the next October...
If you've got an external crack in the block, you may have internal ones also. Keep an eye on the oil condition - if it starts getting milky, you've got a choice to make. You can continue to run it, changing oil when you see a need, and plan on replacing the engine this winter, or you can stop, tear it down, and have a chance of saving what you have. If you've got multiple cracks, you may not end up having much choice anyway.
I had a friend who fixed a hole in the crankcase of his motorcycle with some silicone rubber, I wouldn't have imagined that it would hold up long-term to the hot oil circulating over it, but 5 years later it was still holding strong.
Good luck, and good skiing.
1998 Maristar 200VRS