[Rev]

I think he may have one of those "adjustable shackles" that are kind of long and have multiple "adjustment holes" in them to compensate for worn out springs. They are of only limited "band aid" use.

Get new leaf springs and shocks and new shackles to really address this problem. Look at what's avaiable to decide what you need for your intended use.

Check Mustangs Plus or Canadian Mustangs for availablity and advice. I got my suspension stuff from Mustang Plus in CA. They race vintage Mustangs and seem to know what they're doing.

Rev