Mine is not finished yet, had my grandbabies to help bake cookies and THAT takes priority.
But here goes.

Simple slice on each end, clean up with a sander and glue to the body.

To lower the car, you have to remove these "hooks". They rest on the chassis edges. You will also need to sand the body posts, more on that later.

My bare chassis thus far. It has been sanded all around the outside for clearance. You can compare your chassis to this one and Jesla's and pretty much figure out what we are doing.

Sand the lips off these and file smooth. Then use a small rat tail file and open the holes a little. TEST as you go.
I am working on it still, so no complete photos yet.
Hope it helps.