Might be off the path here a little, but there's a post I answered a week or so ago. There is a company than custom makes springs, might be a source for you.
Also in '86 I was part of a quality group looking at the change in quality of auto manufacture. This was the beginning days of JIT (just in time) processing, QS/ISO 9000, Ford's "Quality is Job 1" program, robotics, outsourcing and etc...
One of the issues is what was termed "Chevette and Cadillac Quality" one of the issues we specifically talked about was inherent quality standards and machining tolerances of front end parts.
One the team members was the purchasing agent that specialized in overseas procurement. A major topic in line with this was poor quality Japanese steel that was coming in at the time. Yours is a '75 which at that time, I believe was still USA sourced steel, but you might want to look at potential (future tense) going tube steel control arms. The Japaneses steel was failure prone under high stress events, which would be in the realm of launch and landings from any wheel stands or other high energy dynamic events.