Will this bolt directly to my existing exhaust pipe?

This muffler has a 2.5" inlet, so it pairs with 2.5" piping. If your current system is different diameter, you'll need an adapter or custom piping — measure your outlet first.

Does this muffler come with mounting brackets?

The muffler itself is included. Mounting hardware and hangers are not confirmed — plan for universal exhaust clamps or custom bracket fabrication depending on your vehicle's suspension geometry.

Can I weld this directly or does it need to clamp on?

Mounting method not confirmed in the product specs. Test-fit it first with clamps before committing to welding — that gives you adjustment room if the angle or position doesn't line up perfectly.