A lot of modern boats have a built in swimplatform. The beam of your boat is probably around 8 foot so the width of the platform will a little less but no less than 6 inchs lees than the beam so around 7' 6".
Are you ordering to fit or just a piece that you will cut to fit? If ordering to fit you will need more information about the shape such as depth from transom to end of platform and any unussual shapes.
1997 2400 SCR
5.7 Vortec / Bravo 2