carpet install help

hello i am installing new carpet in my 67 dart 2dr im not sure how much to cut off new carpet the vehicle did not have carpet in it to use as template.i am missing 2 pieces on each side of the rear seat i believe there is suppose to be trim panels wich i do not have.can anyone tell me what those pieces are called trying to find on internet to buy but everything i search does not come up with those panels.thank you