Do I need to remove the old gaskets or clean the mounting surface before installation?

Yes. Scrape the cylinder head surface clean of old gasket material and debris. A clean, flat surface ensures a proper seal and prevents vacuum leaks that cause rough idle.

What gaskets or seals come with this manifold?

The manifold ships as an assembly. Source new intake gaskets separately — they wear out and reusing old ones is the leading cause of post-install vacuum leaks.

Does this require any modifications to fit, or will it bolt straight to my engine?

Straight bolt-on using factory mounting points. No drilling, machining, or bracket fabrication needed. Torque per your vehicle's service manual once installed.