As this is for a 240RPM spindle with rather low load requirements, I think a sleeve will be a bit OTT. All that is required is for the whole assembly to be as stiff as possible and to be assembled with the least amount of effort. So far two single row AC bearings win on all levels, with taper rollers in second place.

I've found some additional info on CNCzone regarding the fittings of the single row AC bearings, the bottom one against the shoulder should be an interference fit, the top will be a slide fit. Hopefully that's the right way to do it.

Regards,
dsc.