ok, the parts are at my house, I'm gonna get it done over the next couple days depending on weather...I'm putting new pads all around. Should I get all 4 rotors turned? Just the new front ones to be safe? none of em? I haven't really noticed any pulsation, or maybe slightly, but prolly only in the front...should I leave my back rotors go and just turn the LS1 front rotors in case they're somewhat warped?

 

Since you have no idea what the front ones are like, I would have them turned. Ideally you would always turn them when putting on new pads. This gives them a perfect surface to wear in. That said, I have put new pads on without turning if I felt the rotors were still sufficiently smooth and not warped. Any grooves should be machined out.

 

I've heard people suggest to hit the rotors with 180 grit paper after machining to kinda roughen em up (in straight lines out from the center)...should I do that to the rear rotors and not bother machining them? I guess I'll get the front ones turned then get em with the sandpaper too

 

Don't know why you would want to sandpaper rotors after having them turned. The purpose of the machining is not only to true them up, but also to put a specific surface on for wear in. You should only want to clean them up with a solvent.

 

I suggest that you don't do the back brakes at the same time as converting the front to LS1. Do them one at a time. That way if there's anything "weird" afterward you know where to look for what's wrong. It's a valuable lesson that I've learned the hard way.

 

Fresh pads should get fresh rotor surfaces, especially modern hard pads like Carbon Metallic type pads.

 

I had my LS1 brake rotors turned and would highly recommend having it done anytime you change pads. Before you get them turned take the time to clean up the hubs from dirt and rust and use a quality hi-temp paint to make them look nice. Once they are turned it is harder to paint them and not get paint on the rotor brake surface.