i am trying to install a pioneer avh-p4300dvd in my blazer do i need to cut the plastic behind the dash where my stock radio went ? And the guy at the audio store told me i had only a din and a half but the dash bezel is 7inches by 4inches so thats a double din correct ?? Thank you

 

A double Din 'can' fit, but it's not designed to take it. You can search for double din on this forum and find several people that have modified their dash to accept one with good results.