PS: getting back to the topic -
I converted from 763 to 747-100/200 some years ago and, while I liked the 76, I wish I'd done it sooner.
The Classic, with one exception, is by far the most rewarding and interesting commercial bird I've flown.
I miss it.
If you're a pilot in your bones you will love it, 'cos it's a great big, honest, reliable, trustworthy, predictable, friendly tool.
As others have said, polish your three times table and make full use of the years of experience sat behind you and you'll have no problem and lots of fun/satisfaction.
Queen of the skies!