Since journal bearings rely on a lubricant film to "float" the crankshaft, anything that increases the lubricant film strength is a good idea -- & castor increases the film strength. They require more lubrication than a ball-race bearing, but properly designed & installed journal bearings have an almost infinite potential lifetime.

The big risk to BB engines is rear crank-bearing failure -- that will shed chunks of metal into the crank-case, which get sucked up into the cylinder -- often with terminal results. It is not a case of IF the ball bearing fails, it is a case of WHEN it fails. No such problem exists with journal bearings.

Additionally, depending on the bearing material & lubricating fluid, journal bearings are capable of tollerating extremely high rotational speeds -- far higher than any ball-race bearing.