I've read Deakin and Busch too
But I don't recall them saying that a lower RPM gives a longer engine life
for a given HP output.
The big problem with car engine comparisons is that car engines spend most of their life at a very low power, so the reliability of the powerplant as a whole becomes limited by all the ancillaries. Think how often you replace water pumps, hoses, radiators, etc. On a plane, any of these would be a forced landing. The engine itself almost never fails. I recall reading of the Toyota 4L V8 which they developed in the 1980s at a reported cost of $400M. Apparently it has had zero failures and huge numbers have been made and continue to be used. And I've never heard of anybody who has had a
mechanical engine failure in their car.
The only apparent consensus I see is that ~ 65% is a good point to fly at, for a good engine life. It seems to be fairly consistently supported, on the IO360/540 type engines.
Lower RPM should definitely reduce friction losses, and it appears to work better at LOP mixtures, to assist correct combustion timing of lean mixtures. Certainly, my best range is achieved at 2200rpm, full throttle, FL100/120.
I am sure Lyco have the data but they keep it quiet for legal reasons. They face a constant barrage of warranty claims and publishing any variation of operating procedures is an implicit admission of the previous ones being not correct.