Now, let me say I am not replying to your question to Barry. I am only a hobbyist but I really like these discussions.
I reacted to the cost of having your mains bored? Unless there is an obvious alignment problem with the mains, new inserts would be the only thing needed.
There are things to look for on the bearing surfaces. Dropouts or little divets mean they have to be fixed. Ditto a mottled surface with tiny holes. In the absence of these, a good even dull surface shows that they still have life to them.
Shims: In the AD motors, they came with .004" of shimms, a combination of .001 and .002" shims. The official "wear limit" in the specs was .004".
The practise was to remove shims, one at a time on each side until with the rod torqued up to specs, there was interference. Then, you inserted one shim more and that was the adjustment. With the motor apart, this is easier to do because you can swing the rods back and forth.
A good machine shop should be able to do all this for you. There is no need to machine every possible piece of the motor.
