I fail to get this point about 1.3 seconds per evac.
By using the same logic
777-300: 434 seats (and that isn't even the max).
10 doors, half shut off.
87 pax per door.
90 seconds.
1.03 seconds per pax.
With regards to the three engined 747, are you thinking of this?
In which case, this is a 747-300 proposal concieved well after EoS of the 747-100.
I share the scepticism of others as to whether the original 747 was ever planned with a full length upper deck.