Do I need additional hardware to install this clamp?

The clamp itself is the assembly — you'll need a bolt and nut sized for the band's holes. Check your existing exhaust setup or grab standard stainless hardware to match.

Can I use this on an existing exhaust system, or do I need to custom-fab the pipes?

Works on any 2.25" tubing at a butt joint. If your pipes are already mandrel-bent and sized, this clamps them together. If you're building custom, make sure both pipe ends are square and clean for a tight seal.

Will this clamp hold at highway speeds or under engine heat?

Stainless steel handles exhaust temps well. Tighten it down evenly and it'll stay put. For a permanent seal on high-vibration builds, some builders add high-temp silicone or gasket material at the joint before clamping.