Can't speak for the 767, but we practice double engine failures and glide approaches on the 737. I believe the guidlines we use came from a 767 operator.
The best glide seems to be about twice the height for miles to run. 20,000 = 40 miles, plus or minus wind factor of course.
Gear and any flap will be very late when landing on concrete assured. As to how much flap you get depends on what services are available from APU (if there's fuel left), RAT (767) etc etc.
Done it in the sim a few times and survived every one but you sure touch down fast!!!!