it is the same beast if im not mistaken. 5 liters is 300 cubic inches so 60 inches to a liter 5.9x60=354 with my red neck math so give or take 5 cubic inches
1989 d250 muffler delete diaphram turned, fuel screw turned, the lowes special intake
I read that 5.9 liters are really only 5.88 liters anyways...
1990 D-250 Regular Cab: Tweaked injection pump, built transmission, a cataclysmic charlie foxtrot of electronics, the most intense street-ran water injection system in the country, and some more unique stuff.
For a stock bore/stroke (4.02"/4.72", respectively) motor the math works out like this: 3.1416 x 4.02^2 x 4.72 / 4 x 6 = 359.447 cu. in. Cummins calls it a 359, Dodge calls it a 360 and we all call it a 5.9 .
Edit: If you do the same calculations in metric (bore = 102.1mm and stroke = 119.9 mm) you get 5.89 liters.