We always used a rule-of-thumb that you could glide 100 miles after the loss of all engines at 'typical cruise' altitudes. I've never bothered to figure out what sort of l/d that would work out to. IIRC, for all engine out Boeing tells you to maintain an airspeed consistent with the windmill start envelope (which would depend on the aircraft/engine combination). Granted, for fuel exhaustion that won't help...
I don't recall ever seeing or hearing about anything in the FARs regarding l/d or glide ratio - just that the airplane had to be controllable (hence the need for a RAT on many installations).