Hello fellow Houston (LaPort) Dart owner AKA SwingerMan,
Welcome to the board. Sounds like a 73 cast crank j head 340. Check the passenger side of the block for the date. Sometimes it is easier to do if you stick a mirror down there and catch a reflection of it. If all they did is rering it, you have the 8.5:1 low compression motor. You did say "stock rebuilt". Maybe someone with a 10.5 or 8.5 motor will post a compression test number for you to compair to.