Just because the trans was built by ATI does not make it good. I have a ATI converter in my car that broke in 47 runs, got it fixed and is ok now. But I would never have ATI build me a transmission. If you feel more confortable with a 400, ok, but they can explode too. There are better sprags and drums for the 400 that probably should be installed. I installed a Powerglide in my 70 Dart to race Super Street which was not bad, but I am sure the dimensions on a 400 are larger. Then you must fit for a shield or blanket.