Yeah thats what I did. I used my stock shackles.

I looked up the flip kits. Had a question, would my brother have to C notch the frame to run it?

Technically I think your supposed to b/c you will actually get more than 4" of drop. Thats why I would recommend the hanger kit. For what you have up front I think 2 more inches in the rear should be perfect. I would be concerned about a flip kit being too low. Every truck sits a little different and you are already seeing how your truck sits with what you already have installed. If 2 inches more will make it sit where you want it in the rear just do the hangers and be done with it.

I think I'm gonna do that and just tell him to do the hanger kit and see how it looks first before notching the frame and the flip kit. Here's where I am confused. His silverado is a 4 door crew cab. It has the fully welded in hanger in front. Does this need to be cut off the frame and the new hanger goes in it's exact location? Or does it go in a different position higher up? If anyone knows the correct part #'s for my application for 2" lowering hangers please let me know. Thanks so much

Also is running blocks on these trucks in the rear an option?

Yeah do the hanger kit. I did flip kit on mine and added air shocks. I wanted a lower stance and stiffer rear for the torque. So when you push down on the bed it will go down a little but pops up and stops quick. I didn't C notch mine cuz I still have about 3 inches between the frame and rear axle. The bump stops will hit on big dips but it wont slam hard. But like I said my main purpose is to stiffen it up for more power. I also made clamp plates to compress all the leafs together to reduce axle wrap. ITs old school but works.

Blocks are not an option since the leaf sits on top of the rear axle. Blocks can be used to lift the truck not lower it. Some other trucks like S-10's, Toyota's, and Mazda's come factory with the leafs on the bottom of the axle so you can lower them with blocks.

Can I put coil spring spacers in front to help it get a little more height in front. Now with installing the hangers on my truck. Do I cuz the factory ones and put the aftermarket lowering hanger in the same spot on the frame as the stock hanger?

I just measured the front, and it's between 1/2"-3/4" from touching the top of the tire. If I were to remove the drop springs and put back in factory silverado springs how much would the front end go up? Because the rear is 4 inches from touching the top of the tire, so if I do the 2 inch shackle in back I'd still end up stinkbugged running a 1" coil spacer in front and a shackle out back I think. My bro would even rather have it be a little lowering in back than front, just no stinkbug look. That's the worst

It depends on what springs they installed, but usually people will put just the shackles in the back to get an even look. Did they use spindles also or just springs in the front?