I've restored a few and guys have been using JB Weld or Marine Tex for years, and now some companies are putting together repair kits so they can profit. The pc7 is probably a good product but I've never used it. Either of the epoxies I listed work great. Clean and degrease the wheel and use Nytril gloves while working to help keep it clean. You just need to open up the cracks with a file (or cutting wheel if the crack is in a flat area) and end up with a vee shaped groove. Drill small, shallow holes into the sides of the groove so the epoxy gets a good "grip". Sand and reapply and sand until you get the shape you need. Use masking tape to form a mold, if needed, to hold the epoxy in place until it sets up.
Clean and degrease the wheel, sand with 400, clean, degrease and tack rag, prime it, sand with 600, clean, degrease and tack rag, and paint with a good automotive base coat/clear coat or other durable paint.
Dan