Tschall,
JB Weld has sealed a small crack in my 261 block for about 10 years. The 1" crack is above the casting plug on the manifold side of the block.
I first drilled a small divot (hole) at each end of the crack; then v-ground the crack; then cleaned the area very carefully; and finally covered the crack with JB Weld from divot-to-divot.
I'll admit that I think I am lucky, and I expect the leak to recur at any time. However, it was worth a try and it has held up beyond my expectation.
Tim
