Having OIF Bonnevilles, can't agree with comments in this video, other than, yes, the aesthetics are off. Which is a big thing. Some of that was due to tighter legislation, sound and emissions. Although the early OIFs had a pretty conical rear wheel.
Oil-in-the frame dies work, nonsense to say otherwise. It's just one of those things people repeat on the internet. Less oil true, because indeed couldn't be fully filled due to frothing, but better cooling--OIFs do not overheat. Better brakes, discs coming in. So much power in the new 750 bore, factory had to detune them because they trashed main bearings (mistake not upgrading bearings obviously). I'm sceptical they sit 4" higher, although never ridden a 60s Triumph. Apart from the '71 model never heard this criticism before.
Five gears came with OIF.
I've heard from riders who've ridden 60s Triumphs and 70s OIFs, the latter are much more fun to ride.
Anyway, shouldn't say too much in praise of them, otherwise they might get as expensive as 60s models.