My 340 bare block

I would start with another block. Not having the original main caps can be an expensive problem. Those are some odd oil mods, there are plenty of blocks around, may cost $500 or more, but may be money well spent. Good luck with your project.
If the machine work already done is of high quality I'm going to stick with it otherwise it might be downgraded to a lower output machine. My present thinking, though likely wrong.