Using D alkalines and getting 250 lumens becomes pretty difficult because the bulbs that will have that kind of output require less internal resistance than alkalines have.
You could get good results with D Nimh cells, thats 7.2 volts of power and if you put that with a potted WA 1111, you would be over 500 Lumens with 3-4 hours of run time if you bought high capacity NiMH D cells.
Altenatively, you could run a 5 cell bulb on 6 Alkaline D cells for about 120 lumens and a LONNNNG time, just less output.
Bill
Bill