Check with Darryl at RCC Specialty products. He's pretty good with MII front end Cobras. Carrera coil overs work pretty well. 351 size motors use 375# springs.
http://www.dwayne9.addr.com/
Also using late Mustang 8.8" rear, used auto supply store Moog replacement Chevette hatchback or station wagon progressive wound load leveller springs. About $80 for the pair. Since the Chevette wasn't real popular, spring choices are few. Pretty sure this is the only spring available. Works terrific in a Cobra. The progressive wound springs really help the anti-squat characteristics of the car during acceleration, or carrying a load in the trunk.