I feel like I turned a corner here ... having removed the bottom end I found that the bearings were all fine. This is probably the first positive thing I've found so far, lol.

With the worst of the crud removed from the engine its starting to look like something that can be worked with. My Dad has got new fine and coarse stones for the honing tool, so it shouldn't be long before its ready for re-assembly

(pictured in the background is the cleaned up head ... which is FUBAR due to a big chunk missing from the un-machineable port facing I might try and weld it for use as a spare though ...)