Yes, rollcages have been common place since the early '70s and were certainly mandatory before fire proof overalls, which I guess would have been late '70s.
Are not required for MSA club racing, the Morgan runs on standard road seats with an (optional) head rest mounted on the rollbar. A lot of single seaters (including both the F4 cars IIRC) don't have an approved seat/mold either. Having said that a lot of club racers do have high sided side impact protecting seats, they're a brilliant invention and no joke unlike HANS devices I've seen smashes in club racing where they almost certainly let someone virtually walk away from what would have been serious or fatal neck injuries. Certainly the GTR cars need them and any car that is circuit raced and doesn't need to be practical on the road should really have them.
F4 is 40mm and I don't think the ride height is set by the MSA for all event, or at least it has exceptions because it indirectly affects safety and I'd assume is left to championship rules, whatever the MSA regs state a lot of sports racers are lower than that, whether legally or they're just never checked I don't know.