Look at maier suspension.
https://mikemaierinc.com/ I am running his complete coil over setup in the front AND rear. It's pretty trick. Easy install and he has stuff for these 71-73 cars. I also looked into Street or Track (Shawn is the owner). His stuff is nice too. I went with Maier because he actively tracks his products and is at way more events than Street or Track. Also.... the owner (Shawn) was very rude to a buddy of mine who was looking at spending a lot of cash on a full front and rear setup. When I called several times to ask technical questions and had a few quotes made up for my car (also for a complete front and rear setup) he was also rude to me when I was trying to Taylor the kit for my needs. So he won't get any of my business.
Different story with Mike Maier. Thise guys are awesome. They are busy and a small shop so have some patience. Their stuff is quality, they use serviceable parts and is genuinely a top notch product. They offer different kits for our cars depending on how wild you want to go. I'm running their cantilever coil over shock setup (that actually places the shocks horizontally in the trunk of the car) on a floating 9" in the rear. They have awesome leaf spring packages and a different cheaper 4 link setup as well.
Total Control Products also makes a kit, saw that one in person. Not a bad kit. Maier was better though in overall fitment and in the tech support area.
Just my .02
Sorry for the typos, doing this on a cell phone.