'That was the last time Harley-Davidson had a new idea.'
ROTFL, that one made my day. So with you on that, I loathe HD simply because they refuse to exit the thirties in design. But then I was whuppin' up on 900 Sportsters in the '70s on hot 400 cc. bikes.
Yes, Herbert made rollers long ago, I refer to the OEM doing it though. They do nothing without good reason. The rollers they made were stock acceleration ramps too until they started using the idea further on hotrod like Camaro, Vette and Mustang engines. We used to be W/D on General Kinetics rollers back in the '70s.
The second resurgence of HP in the 80s makes sense if combined with the emissions idea as well, the feds passed law saying the cars must hit emissions for 50,0000 miles and they still wanted more power to combat the other car makers, the two fit together. If you make hi-po car it as well must pass the emission spec.
"What I haven't discovered yet is why newer bucket followers don't seem to suffer."
If referring to modern 16 valve engine buckets, it's the weak -ssed springs, you can easily push a valve half lift by hand. Not enough load to wear the bucket or shim. Bucket also still spins, the half lobe on one side ala zetec. Cam is full width lobe only part way round. ALL cams including OHC must have clearance at some point if mechanical (the 2.0 does), the lobe is lubed by that. Juice lifters technically have clearance, loose enough that they still do not wipe lobe absolutely clean of oil. They tighten up internally on compression. Why they don't hold the valves open. Modern day buckets and/or shims on top of them are heat treated now enough to let solid lifters run forever with virtually no maintenance at all. No lead in fuel and engine design have allowed the valve recession rate to about equal the tappet/lobe wear rate to let the clearances stay the same forever. Often now the clearances close up instead of get looser like old school, the valve recedes more than the wear on bucket. Why exhaust valves on buckets are so dang loose now (zetecs set up to .013"). There are issues with cams rocking around in cam cap clearances too to alter clearances at valves too. All that bucket stuff from the Japanese hotrod bikes, been doing that for many years. Working on a '02 zetec just like working on my old Honda CBF bike in 1980.
Zinc removal didn't happen until maybe 95-00 or so, not the zinc so much as the carrier of it, the phosphates (zinc dithiophosphat e). EPA started a war on roadside phosphate pollution around then.