The change to IFS would be a good question for the Prevo techs this winter at West palm beach.
It happened during the mid 90s if u get my drift. As one general rule the Hs often got the changes first.
For example there r many mid 90s chassis with Rockwell disk steer brake, drum drive brake and knore bremse disc tag all on the same chassis.
Another thing you're going to be surprised to see Prevost used stud piloted hubs and rims for almost a decade after the trucking industry started moving to Hub piloted I work on lots of O2 and O3 buses that still have stud piloted hubs and rims.
This is Pier at work