727 speedometer gear

Hey guys, I put a 440 with a 727 trans into my 70' Dart now my speedometer is off. My tire size is 245-60-15 and my rear gear is 3:55, according to the chart in the Yearone catalog I'm looking for a 36 tooth (RED) gear. If anyone has one or better information on how to make sure that I get the correct gear it will be greatly appreciated. I currently have a 29 tooth gear (BLACK) and I can tell you it reads way faster than what the car is moving. Thanks Dave!!!!!!!