The only thing to significantly change for main/rod bearings is the ease at which they can be replaced. Yes, they still run on babit material, but other than checking the journal for wear you really just replace them.. no molds/fitting/scraping etc. You can get a complete bottom end done for the cost of the bearings is all are in spec.. that's maybe $100-150.
But the to pay shop rates to have all that babit work done... yeah.. you gotta WANT the original to be able to justify it.
Plus that older thick babit could embed a boulder and still run. Now a days 20-30 micron particles wears it all out.
If you changed the oil, ran filters (both full and bypass) and and keep the RPMs under 2000-2500 I don't see what's stopping a properly done babit motor from lasting 50-75k or more.
The whole problem is that it can cost you (as mentioned) a very pretty penny to do it.
I've always wanted to take a scraping class... and I have done some very small projects (some smaller gibbs, and vices) but there is a lot to it when you get into the minutia of it. Its still done on higher end machines... there are lots of youtube videos showing how to do it.
