valhalla74,
I would strongly recommend that you remove the dash from the car to install the dash pad. With the compound curves around the instruments and at the outside corners by the doors, and bottom edge of the dash, it would be a nightmare to get a good fit.
The pad needs to be stretched and secured at many points while forcing it to the metal dash's shape to ensure the adhesive holds. On a work bench or a purpose made stand its challenging enough. While still in the car ... I wouldn't even think about attempting it, especially if I expected a professional looking result.
I worked for three years in a small bird restoration shop, and the boss always tackled this job with the dash on a purpose made stand, and even then it was a bit** of a job.
Gene