OK -Coil spring info here. Probably more than you want to know. The link from Desert_buick to Fatman provides Napa part numbers. Here is the break down including Napa part number/spring load lbs./spring rate lbs./ year and engine of MustII.
#277-3036/ 1388/353/'74-'76 Must II &'78 Pinto wagon 6cyl
#277-3037/1265/324/ '78 4cyl
#277-3038 / 1561/364/ '74-'76 4 cyl & 6cyl
