This should get filed under the “Ideas that I have but won’t get around to messing with for a really long time” category.
It’s pretty simple start off with Swords & Wizardry White Box then throw a bunch of the stuff by Barrel Rider Games then use a bunch of the great random generators like the d30 books by New Big Dragon Games and/or stuff like Wizardawn.
Then just roll up characters and start adventuring. Now predetermined ideas about anything just whatever comes up in play. Just worry about the places the characters are from, where they are at, and where they are going. That’s it. Let the dice and whatever random inspiration that pops up from the players and the GM take it from there and see what happens.
Yeah, you could use just about any game to do this but hey keep the game simple because there will be plenty of other things to put your mind to when the dice start rolling.