[Phantom]

Does the Buick have a bench or bucket seat? The only reason I ask is it will be easier to do neutral coasts if you have one of the few bucket seat versions.

If the shifter is on the tree see if you can easily pop it into neutral from drive without pulling in on the shifter or skipping past N to Reverse. The Bonneville I had with it on the tree did not always stop at N and went in to reverse shutting down the engine or if slow enough jerking it to a stop. But remember I was 16 at the time of doing that so it could have just been me pulling back on the leaver and forcing it into Reverse.