Do these headlights plug directly into my truck's wiring harness?

Yes, these mount at factory connection points with no harness modification. Your existing electrical setup connects without adapters.

Will these fit if my truck has been restored or modified?

These are engineered for factory mounting on the 359/379/389 chassis. If your truck retains original headlight buckets, these will bolt in. If you've swapped in a custom front end or non-factory mount, test-fit before finalizing purchase.

How long do LED headlights typically last compared to what I've got now?

LED units run significantly cooler and longer than halogen. You won't get a specific hour rating without manufacturer specs, but the reduced heat and solid-state design mean fewer replacements down the road.