Quote:

...turned out to be a split cylinder wall.

I would like to just transfer The parts I have to the new block

What were the cyliner wall thickness numbers from the sonic test?
The availability of the MP blocks (World Products) comes and goes. Since you want to use your pistons (4.3xx"), you will need the smaller bore blocks and sometimes only the larger bore (~4.5") are available. Koleno is an option, slightly more expensive from what I have seen posted.