At this point, since the head is no longer usable for a cooling system pressure test, it would be best to do a complete tear-down of the block. Once the block is bare, you should either pressure wash it or clean it as well as possible and then use compressed air and some soapy water to check suspected areas for cracks or rust-outs. While disassembling things, it's a good idea to inspect each part so that you will have a better idea of what will need to be replaced.
Tom
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