Might buy a 340 block...

There are quite a few cases of thick cylinder walls in the first production runs of 360 castings. It was confirmed that 340 cores were used for the water jackets until the bean counters noticed the expensive high nickel iron was being used up faster than it was supposed to be. Correct on the main webbing, all 360s came with a standard design for the larger main bearing size with two bolt retention. At one time there was some internet speculation that some of the early HD 360 molds used web sections for T/A pass car blocks but after looking closer again it turned out to be an internet myth. Or at least until someone comes across one, which I do not expect to happen.