The front doors of my 90 have never been exactly right. Particularly the passenger side, which doesn't shut properly at the bottom up to the body curve. The drivers' door rattles a little in the wind, but that's probably normal.

Tinkering with the hinges/door striker has helped somewhat, and new hinges without worn pins helped more, but I can't seem to eliminate the gap at the bottom. Without taking the top half of the body off, what's the best fix? Is it basically a case of grabbing the top, deploying a knee at the bottom, and pulling?

It's what they did at the end of the production line so probably yes.

My 2nd row doors didn't fit at the top either. After messing and trying to bend flush I opted to fit a 3mm strip to the outside edge of the roof (above the door). Then fitted a new seal - it had to be hammered in place but the door is a tight fit. The strip was attached by simply using a small piece of gorilla tape.

See attached

That one's a classic