It is the same age as your grandma but much faster and much, much, much more expensive... Doesn't have eight figures price tag only if you pay for it in bitcoin
But of course, it's 250 Testarossa!
The car for Assetto can be found using the link. After doing that myself I ended up spending days tinkering with everything that comes in unfinished state. Including the physics...
So, to install and see what I'm on about extract the contents of this .7z into "..\content\cars\" subfolder of your game and confirm the prompts. It applies the aforementioned collider, lods, CSP config and physics to the car that you must have and already tried. If you want to have the original physics easily available - first rename "data.acd" to "data.acd1" and it will not be overwritten. To switch to it simply rename mine to "data.acd2" and revert the old to "data.acd".
For better immersion I recommend replacing the sound with the one from "Ferrari 330 P4". Here is what gives me that idea.
General tips: when you feel the feedback from the car weaken as you lose track of time it may be the tires are worn, fuel is burnt out, track's condition worsened or your wheel's motor got hot (most likely all that, combined) - don't hesitate to reach for that Numpad "+" on your keyboard. In real life your natural reaction would be heightened awareness to the "seat of pants" feel but in the sim the only effective way to simulate that is to have good level of feedback on the wheel.
Have a happy driving!