Like Ian Parsons I too have resorted to the cylindrical grinder in the past, it does work even if it seems drastic, but it requires a lot of care and if you’ve not got a good grinder in the shed, expensive! The down side is the possibility of even a small amount of distortion being introduced into what is a very accurately made item with little room to accommodate any such shape changes.
But all is not entirely lost. What about using a standard 6006 bearing and making steel sleeves to make up the difference?
The 6006 principal dimensions are 55 x 30 x 13. It has a quoted dynamic load rating of 13.8kN which should be plenty surely?
In order to use the biggest undersize bearing the re-sizing sleeve thickness needs must be kept as thin as possible and I’d suggest using something a bit better than standard mild steel here because of that. Maybe something like 080M40 might do the business.
The benefits? The 6006 bearing is a standard size and therefore comparatively cheap. With access to turning facilities producing the sleeves is a straight forward and cost effective turning exercise, with a bit of care and a drop of the Loctite type adhesive it should be problem solved.
And best of all you have made no changes that cannot be reversed.
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