Do both springs have the same amount of leafs on both sides or are there different numbers leafs on both sides? If more leafs on one side than the other the left side(drivers side of the car) gets the most leafs on Hi Po Mopar OEM and the after market Hi Po replacement springs from Mopar
As far as finding that spring number and its original car that it came on it is a early car by looking at the early stamp number(28------) on that leaf, probably pre 1968