Forget it.
You can't go from 60i or 60p to 24p without pain.
(Shooting 60 for slomo is of course a good idea...)
Think about it, you need to trash 36 frames every second.
You could go to 30 quite easilly, by removing every other frame...
But most imporant, what is your delivery?
If it is DVD, bluray, broadcast or internet, there is no reason NOT to use 30 (or 29.97)
This way you can go from 60p to 30i, and you'll get the best of all worlds.
I've never understood why so many people want to shoot 24 if their final target is 29.97, and i never understood what people have against interlace. IMHO it is just great. Full res at still parts, double the framerate at moving parts.
Bouke
www.videotoolshed.com