Never really looked into it all that much, but here are the spec's on some OEM coils for the front end of a F150

Coil Spring Free Height : 16.74" Driver Side/16.06" Pass. Side
Coil Spring I.D. : 3.812"
Coil Spring Load Height : 11.5"
Coil Spring Type : One Tangential End; One Pigtail End
Design Load : 1500. Driver Side/1625 Pass. Side
Spring Rate : 285 Driver Side/357 Pass. Side
Wire Diameter : .656" Driver Side/ .672" Pass. Side

The spring rate difference between driver and passenger side is 72. I'm assuming this is to account for the torque of the engine in the big trucks. I would think that if you pulled the driver spring out of 2 rigs that you would only have 80% of the stiffness.

** These would be for a 1975 1/2 Ton

 

1997 Thunderbird
Coil Spring Free Height : 16.88"
Coil Spring I.D. : 3.677"
Coil Spring Load Height : 14"
Coil Spring Type : One Tangential End; One Square End
Design Load : 804
Spring Rate : 290
Wire Diameter : .656

 

1986 Cherokee
Coil Spring Free Height : 18.4"
Coil Spring I.D. : 4.04"
Coil Spring Load Height : 15"
Coil Spring Type : One Tangential End; One Pigtail End
Design Load : 503
Spring Rate : 152
Wire Diameter : .578"

 

1993 YJ
Coil Spring Free Height : 18.4"
Coil Spring I.D. : 4.04"
Coil Spring Load Height : 15"
Coil Spring Type : One Tangential End; One Pigtail End
Design Load : 503
Spring Rate : 152
Wire Diameter : .578"