You're gonna have to find a stamped number to tell what you have. You can tell a 170 from a 225 by measuring the bypass hose. It will be roughly 3" on a 225 and half that on a 170. Since your Dart is a '70 though,, it will have either a 225 or a 198. Since these engines use the same block, the difference in the bypass hose is not valid and you are going to have to find the engine number that is stamped in the block deck behind the alternator bracket. There is a flat pad about 2 inches long and 3/4 inch wide that is not covered by the head. The number starts out with 2 letters, 3 numbers, and another letter followed by a partial VIN number from the car. AA225A for a 225 and AA198A for a 198. Chances are you have a 225 since the 198s are scarce as hen's teeth. The 198 is worth a lot more than a 225 just because of the rods. Hope this helps.