Since the Atomic 4 is very similar to the Model A Ford, i.e., flathead 4 with cast water jackets, the following technique would probably apply.
At both ends of the crack - or even 1/4 inch beyond - drill a stop hole, which will prevent the crack from propagating. Thread this hole 5/16-18. Screw a 5/16-18 screw into the hole, and cut it flush and pein it over to prevent rotation. Next, drill a #7 or 13/64 hole overlapping the filled stop hole by about 1/3 of it's diameter, and tap it 1/4-20. (When I've done this, I've started ALL of the holes using a small Center Drill. If you don't know what this is, you might not want to do this.) Thread a screw into the threaded hole, cut it off and pein it, as well. (A short piece of all thread rod may be used for this.) Pein the end over lightly to prevent it from rotating. Next, add a hole adjacent to the hole with the threaded insert, overlapping it by about 1/3 of the shank of the insert. Do this from one end to the other, connecting the two end holes, which will be threaded 5/16-18. As the screws are being inserted, you may also use Loctite Thread Locker to prevent rotation if you don't want to peen the ends over.
This was the technique mechanics used in the '30's & 40's to repair engines without removing them from the car, assuming the crack was in a location where the drilling & threading could be done. I used this technique in the '60's on my first car, a 1929 Model A Ford...
Take nice pics and post them here!