OD&D campaign to begin?

This may be it... the campaign that I have been working and re-working and tweaking and re-combining, and occasionally even playing bits of, may be about to begin again.

Of course, I can't play the campaign with people my own age (not anyone who's interested in D&D anyway) because, well, they're the same age as me, and interested in D&D. They've already read all the WDs from 48-98 and the Imagines from the same period (as long as they lasted anyway), they know what the Key of Tirandor and the Tower of Mylakhrion are, they know that 'Bree Yark' isn't Goblin for 'I surrender' and they know that under no circumstances do you put a chip of the stone from Zelligar's dungeon in your mouth. But...

My teenage son and some of his mates have expressed an interest in playing some D&D. Now, while they might have something like 4th Ed in mind, I don't know what 4th Ed is all about. If they want me to DM I'm happy to, but what they're gonna get if they do is an OD&D mash-up - a combination of the early 'dungeoncrawl' style with the slightly later 'ecological dungeon' approach. Because that's what I played when I used to do this back in the early-mid 1980s.

There are some things to be worked out. What is the campaign world actually going to be? There are four main possibilities, with some subsidiary questions depending on the first results. Will it be the homebrow-of-Mystara (of course, I didn't know it was called 'Mystara' at the time) world that I originally attempted to place all of these adventures in, or perhaps the slightly later homebrew world of my own devising that didn't have Arabs and Mongols and Greeks and Venetians all living next to each other? Or, perhaps, Middle Earth (but then, the ICE TA1600s setting, or the War of the Ring period, or into the Fourth Age?) Perhaps a cod-Arthurian campaign, with Orcs and Dragons in Dark Age Britain (with, at the same time, knights in plate-mail?) Then again there's always Discworld as option.

All present certain challenges. Well, we'll see, perhaps...