Any reviews on a 360 magnum crate motor P5249499

hi all I just bought this Mopar 360 crate motor part number P5249499 from a guy who never got around to putting it in his duster .It’s going in my 71 dart with a 727 tranny and a 8 3/4 posi rear with 373 gears and just wanted to know if anybody used this motor in a A body and where you satisfied with its performance.thanks Also I’m confused about which flex plate to use .mopar tech support says use the external balance one ,but I noticed that some come completely round and others come with the half moon cut out type.l need help on this one thanks all .