It sounds like the block is cracked and you know where to go from there.
If it is only leaking externally, you stand a chance.
Dunno if JB would work or not, but it has performed miracles in the past and it beats the alternative.
Personally, if it were less than a dribble, I'd go the cheap route and not stray too far from shore until I had confidence in knowing what was going to happen.
I've run worse, but it always got me back to the pier.
Nothing is so broken that Government can't make it worse.
Honestly, the block is cracked and its in a high stress point (head bolt). At this point, I see very little to lose by trying JB Weld but I fear it will be a short lived "fix". The real fix is going to be a new block at some point.
I used the two part JB weld epoxy this weekend on the cover plate at the end of the exhaust manifold. It was leaking water thru a newly cut gasket so I cranked the 4 bolts tighter. One broke flush with the housing. I removed that cover, removed the gasket, slopped on the JB Weld and it's held well, no leaks. The plate will never be removed again anyway since a new manifold is the goal, somewhere, some time.
What do you have to lose? There might be some high temperature cast iron repair JB Weld type products out there that might perform better/longer?
or ya could go see your local welder. i have a block in similar shape. a local welder said he could fix it if i brought him a stripped bare block.... said i could leave the brg.s in it though..... i've not done anything with this block as i think it's junk. anything i do would be, maybe it'll work. and i don't want to take a chance on maybe....