The Monogram Thunderbird will work perfectly. The wheelbase and track width are perfect. Only a minor alteration to the front and rear of the chassis along with making a tray interior and mounting posts will be needed to mount the T'bird on the Monte Carlo chassis. The T'bird kit comes with vinyl press on stickers for Donnie Allison's car.
Now that the 2019 scaley line has been announced with the T'bird I am debating about making the conversion.