Farmer J: What you're seeing are typical cracks on Model A's.
Depending on your block but generally speaking they are approx 3/16-1/4" thk.
I would recommend cleaning the block and looking it over thoroughly, there may be other cracks than ones you've already noticed which are common.
We repair cracks through "metal stitching'' and speak from experience to say check block thoroughly for other cracks.
The cracks you mention are from freezing.
Enclosed two photos of the areas you have described and recommended permanent repair "NOT Jb weld."
http://www.jandm-machine.com/metalStitching.html