Reimagine revival stories under the budget of original Who?

It provides nostalgic items that help with the celebration of the show's history including River's heels, as well as a board with pictures of the Doctor's past companions. A classic series Day of the Doctor would likely have been a celebration of the show's history from that point in time. With Sarah Jane the timing would admittedly be unfortunate however given it would only be a year after the last celebration - The Three Doctors - and no anniversary to celebrate either.

1948 wasn't it?

I was suggesting the England World Cup event that took place in 1966. It would have been set in the future, as was Fear Her.

If all else fails, how about the London Olympics in 2068? Close enough for you not to go full TV21, but far enough away for plausibility.

Well... If we chuck out The Time of the Angels / Flesh and Stone because that makes a pretty good four-parter as is, you could very easily condense The Impossible Astronaut, Day of the Moon, A Good Man Goes to War and The Wedding of River Song together into a single story. The rest feels very much like killing time before the climax, you could argue that even A Good Man Goes to War is unnecessary.

I think the only way it could really work in the context of a classic serial is if you did something like The Keys of Marinus. Although that said, there would be a distinct The Invasion of Time feel at the end with the sudden alternate universe swerve. Film footage shot on location would probably be cut down to the assassination on the shores of Lake Silencio, if not recorded onto video to save on costs. A lot of money would probably have gone into the Silents' heads, making the rest of their costume look rather shabby by comparison. Actually, considering that all the spectacle would be ripped out, it's likely that it would look a very bare bones serial.