http://theoldmotor.com/?p=48557
I'm amazed at how many people think that babbit is some sort of ancient alchemy or witchcraft. Most (nay, 99%) of the people don't know that even today, babbit is used in engines... but on easily replaceable 'shells' rather than having to be poured then machined.
Babbit main bearings can use shells (like the article) or be a little different there are no shells and you pour babbit directly into the block. You still have to provide oil holes and then line bore... but its really not rocket science.