We had a world class manager, and it got us to 5-8th in the league consistently. I'm not sure that Porto is a valid comparison, as whilst they may be relatively small compared to the giants of European football, they are nonetheless one of the giants of Portuguese football, so can probably have their pick of the best Portuguese talent before they're snaffled up by bigger clubs.
The same applied to the great Ajax team of the 90's. Sadly, the same does not apply to us, as we compete with a lot of clubs for the best young talent in Britain.
The only real hope we have imo is to have an influx of 6-7 young players of England quality around the same time. I've bemoaned on here at length how average our own youth production line is, but of course England as a whole does no better. That sort of situation used to happen a decade or so ago, with the likes of Leeds, West Ham, Man Utd and even Liverpool having a crop of talent coming through at the same time. I can't think of any teams that have had any in the last 5 years.
That's all it'd take though (I know - 'all' it would take), but drop 3-4 England international quality players into our squad and it would be competitive at the sharp end of competitions. It'd certainly be top 4 material.