I looked at a site for torrington bearings and the cage has to be a press fit, so really no retainer would be needed. The ball is supposed to be partly full of lubricant, so keeping bearings lubed shouldn't be an issue. I don't think it's something I'd be tackling, as I don't have the machine tools to do it. I did see that a 17mm bearing would be a good fit on the pins, but don't know about in the yoke. The 17mm bearings have a cage about an inch in OD.
One fly in the ointment is the groove in the pins (see the pic above) that extends about half the length and might tend to eat up the rollers. I'm sure a roller wouldn't like coming to an abrupt edge.
