Assuming that you are using the Alpha B24J as mission 5 calls for, you only need to change the the tail gun parameters in the dp's gunstations. What i've done with mine is modify the tail gun setup to represent a hybrid between the stock twin 50's and the Betty's single 20 mike. The parameters to modify are in red:
Here's the stock Betty:
[GUNSTATIONS]
gunstation.0=0,51,1,0.06,750,2,0.01,600,0,40,1d1*11,0,0,6.217,0,0,0,-25,25,25,-25,0.4
gunstation.1=1,52,2,0.12,555,2,0.01,1000,4,40,1d1*30,0,1.589,-2.526,0,0,0,-180,180,80,0,5
gunstation.2=0,54,1,0.06,750,2,0.01,600,0,40,1d1*11,-0.877,0.225,-6.14,0,0,-90,-75,75,75,-75,0.4
gunstation.3=0,55,1,0.06,750,2,0.01,600,0,40,1d1*11,0.877,0.225,-6.14,0,0,90,-75,75,75,-75,0.4
gunstation.4=1,57,2,0.12,555,2,0.01,1000,4,40,
1d1*30,0,0.001,-13.873001,0,0,180,-25,25,25,-25,5
gunstation.5=3,21,8,0.00,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
gunstation.6=5,62,32,0.00,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
[guns.0]
gun.0=1000,0,0,0.957000000000001,0,0,1,1000
[guns.1]
gun.0=1000,0,-2.89999999999999E-02,1.102,0,0,1,1000
[guns.2]
gun.0=1000,-0.848,-6.00000000000001E-03,9.99999999999446E-04,0,0,1,1000
[guns.3]
gun.0=1000,0.848,-6.00000000000001E-03,9.99999999999446E-04,0,0,1,1000
[guns.4]
gun.0=1000,0,0.001,-0.907,0,,0,1000
[guns.5]
gun.0=32,0,0,0,0,0,0,8
[guns.6]
gun.0=1,,,,,,0,
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Here's the stock Alpha B24J:
[GUNSTATIONS]
; Starboard Cheek Gun
gunstation.0=0,50,1,0.08,870,2,1,274,2,40,1d1*18,0,0.2,6.5,-0.19819,0,0,-90,90,60,-60,5.184
; Upper Gun
gunstation.1=0,52,1,0.08,870,2,1,274,2,40,1d1*18,0,2,0.8,-15,0,180,-180,180,65,-15,5.184
; Port Waist Gun
gunstation.2=1,54,2,0.08,870,2,1,274,2,40,1d1*18,-0.5,0,-7.6,15,-110,-110,-90,70,70,-70,5.184
; Starboard Waist Gun
gunstation.3=1,55,2,0.08,870,2,1,274,2,40,1d1*18,0.5,0.35,-7.8,-5,0,110,-70,90,70,-70,5.184
; Lower Gun
gunstation.4=1,56,2,0.08,870,2,1,274,2,40,1d1*18,0,-1.45,-5.2,5,0,180,-180,180,0,-90,5.184
; Tail Gun
gunstation.5=1,57,2,0.08,870,2,1,274,2,40,1d1*18,0,1,-13.25,-15,0,180,-15,15,45,-45,5.184
;
gunstation.6=3,21,8,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
[guns.0]
gun.0=400,-0.28,0,0.68,0,0,1,400
gun.1=400,0.28,0,0.68,0,0,1,400
[guns.1]
gun.0=400,-0.2,0,-0.68,0,0,1,400
gun.1=400,0.2,0,-0.68,0,0,1,400
[guns.2]
gun.0=350,-1.15,0.05,-0.25,0,0,1,350
[guns.3]
gun.0=350,1.2,0.1,0.1,0,0,1,350
[guns.4]
gun.0=400,0.35,-0.186,-1.212,0,0,1,400
gun.1=400,-0.35,-0.186,-1.212,0,0,1,400
[guns.5]
gun.0=400,-0.45,0.1,-1.23,0,0,1,400
gun.1=425,0.45,0.1,-1.23,0,0,1,425
[guns.6]
gun.0=16,0,0,0,0,0,0,0
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Here's my Alpha B24J mod:
[GUNSTATIONS]
; Starboard Cheek Gun
gunstation.0=0,50,1,0.06,890,2,1,1000,2,30,1d1*38,0,0.2,6.5,0,0,0,-90,90,60,-60,1.6
; Upper Gun
gunstation.1=0,52,2,0.06,980,2,1,1000,2,30,1d1*38,0,2,0.8,-10,0,180,-180,180,65,-15,1.6
; Port Waist Gun
gunstation.2=1,54,2,0.06,980,2,1,1000,2,30,1d1*38,-0.5,0,-7.6,15,-110,-110,-90,70,70,-70,1.6
; Starboard Waist Gun
gunstation.3=1,55,2,0.06,980,2,1,1000,2,30,1d1*38,0.5,0.35,-7.8,-5,0,110,-70,90,70,-70,1.6
; Lower Gun
gunstation.4=1,56,2,0.06,980,2,1,1000,2,30,1d1*38,0,-1.45,-5.2,5,0,180,-180,180,0,-90,1.6
; Tail Gun
gunstation.5=1,57,2,0.05,980,2,1,1000,2,30,1d1*38,0,1,-13.25,0,0,180,-35,35,45,-45,1.6
;
gunstation.6=3,21,8,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
[guns.0]
gun.0=400,-0.28,0,0.68,0,0,1,400
gun.1=400,0.28,0,0.68,0,0,1,400
[guns.1]
gun.0=400,-0.2,0,-0.68,0,0,1,400
gun.1=400,0.2,0,-0.68,0,0,1,400
[guns.2]
gun.0=350,-1.15,0.05,-0.25,0,0,1,350
[guns.3]
gun.0=350,1.2,0.1,0.1,0,0,1,350
[guns.4]
gun.0=400,0.35,-0.186,-1.212,0,0,1,400
gun.1=400,-0.35,-0.186,-1.212,0,0,1,400
[guns.5]
gun.0=400,-0.45,0.1,-1.23,0,0,1,400
gun.1=425,0.45,0.1,-1.23,0,0,1,425
[guns.6]
gun.0=16,0,0,0,0,0,0,0
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Its still essentially a twin 50, but with a dice of 1d1*38 per gun, a range of 1000 meters, a muzzle velocity of 980 m/s and an 0.05 rate of fire (20 rounds/second) times 2. I think its a pretty fair equalizer in comparison to what the Betty packs. My left-right swivel limit is 35 degrees and my elevation and depression limits are both at 45 degrees -- that's a very generous arc of defensive coverage for a bomber's six.
Go get 'em!!!