well....FWIW....I just talked with the folks at Castrol, and they said the only oil they currently make with the anti-wear package for flat tappet camshaft engines is their 5W50 Edge.
I also called the Quaker State tech line...and the recorded message said 'welcome to the Shell Corporation', so yeah. Then I asked their tech dept and they said they acquired both Quaker State and Pennzoil - both now based on Shell oil...so there's that.
Shell re-stated that their Rotella T4, 5 and 6 diesel oils all 'were' APISN rated, which has been since reformulated again to include the necessary ZDDP package for flat-tappet diesels (and gas engines), and that their gas engine 5W30 oil...formulated for vehicles with cats...does not.
According to Shell, it is the combination of the gasoline exhaust with the phosphorous that kills catalytic converters, whereas diesel fuel exhaust does not have the same deteriorating effect. I of course can't confirm whether or not that is scientifically accurate but I suppose it is still a potentially plausible explanation.
Also, according to Shell...all of the Quaker State and Pennzoil oils now produced carry the APISN rating, meaning not higher than 800 ppm of the anti-wear additives...meaning none of them are recommended for flat-tappet engines.
With all of that said I am pretty confident in the Rotella T oils, and Castrol Edge 5W50.
Just passing on what the tech folks are sayin' - hope it helps.
- Sam