Brian,
Its interesting you seem to like the ball bearing main.
Beeza Bill had a ball bearing main in his A65 which covered a hundred billion miles with no problems. (RIP)
and there's a couple of interesting ball bearings floating about these days.
They are designed for use in transmissions which seem to have a rough life and are prefixed TM or TMB.
The most interesting one is the NTN TMB206JR2C3. This bearing is also used by KTM and Husaberg in their bikes.
Apparently they replaced a roller with this in the Husaberg as the roller kept breaking down???
google it and have a look.
If you read NTNs blurb, while the dynamic load stays the same, the life is 4 times better.
http://www.ntnamerica.com/pdf/Other/tmbspec.pdfThey even claim its a replacement for a 6306. I'd love to get one with a seal in one side.
Another one is the NSK TM206C3. This bearing has special seals to let oil in and keep particles out.
I've got one of these sitting on my desk. There is a temptation to fit the thing as the drive side main as its impossible get a sealed NTN in Aus for love or money.
Feel better after getting that lot out, time for a beer.