Accidentally made 12 instead of 6 (don't operate Cura late at night, folks).
This uses the settings for the LM8UU bearing. I had to play around with the 'sd' variable a little to get it to grip but once I had it dialled in, it works great. The setting I used was 0.4.
Experimenting with different parametric bearings at the minute but they all seem to work very nicely.
The cost/weight savings so far look promising: 12g/£0.31 vs 52g/£1.20 for the originals (weight & price including bearing, printed versus the LM8UU).
Printed these in PLA but intend to try other materials for comparison.
This is the longest (13 hours) print I've done so far and was a little wary of leaving it overnight but the little A8 seemed to handle it well. Only noticed one or two minor artifacts and next to know stringing, three in total, I think.