Upper & Lower Control Arms for 1970GMC C2500 2WD with 1972 Knuckles

[SonomaComa]

I purchased a 1970 GMC 3/4ton 2WD Long Bed 350cu with Front Coil Springs and Rear Leaf Springs. The previous owner installed 1972 Knuckles in it for a front disc brake conversion. To install the Steering Knuckles he said he only replaced the Upper Ball Joints built for a 72 because the taper is different from 1970.
The front end leans to the right a little bit. I was going to just replace the coil springs but noticed the Lower Ball Joint on the right front Lower Control Arm is welded in! Now I need to replace that lower control arm. Might as well replace all Upper & Lower Control Arms but where can replacements be found?
I could not find any Uppers, only Lowers for 1971-1974. Aren't 1969-1972 all the same except for the Ball Joints?
http://www.summitracing.com/search/p...5-c2500-pickup

On that link 2 are Standard Duty and only 1 is Heavy Duty. S.D #CK6553 & #CK6555. H.D #CK6554. What's up with that?? And only from 1971-1974