I was told that ls6 heads are a direct bolt on to my 99 chevy silverado 5.3. Is this true? Any mods that need to be made? Any surprises I could expect? Thanks for your help!

 

Yah they are a strait swap, will give ya a more over stock...
John

 

they will flow more air but you will loose a lil bit of compression, you can have the ls6 heads milled to keep your compression up

 

check with patriot performance they have great deal on LS6 heads stock milled back down to a 61. Originally they have a 64 chamber and thats where you would lose the compression. I am about to do the same thing myself and patriot had the best price.