I think a lot of those oil specs were also because of the MDS, not necessarily clearances. The MDS system was pretty picky on oil weight and would give people issues when they ran thicker stuff at least from what I recall reading. Not that bearing clearances couldn't play into that, but I know a lot of the banter came from MDS. Bearing material might have something to do with the clearances as well, but I'm by no means an expert or even all that well versed in bearings. Modern street cars tend to run aluminum bearings though, which I could see maybe having tighter clearances due to being marginally softer maybe?