69 c/20 rear axle set up

[recboy300]

hello i am new to the site and like all the great info thats hear. that being said can anyone give me a direction togo i have a 69 c/20 and the rear diff is a coil under set up how would i go about putting leaf springs on it and a newer axle.i am only thinking about this because i cant find 3.73 gears or lower for the one i have. i think it has 4.56 now but not good for highway use. any help is greatly welcome thx