Trans swap

You will have to do major surgery on the trans. tunnel to make the 518 fit in the Dart. I'm not sure but you may even have to modify your crossmember to make it fit. Also figure on having the driveshaft shortened. The 518's OD unit is huge in comparison to the tailshaft on a 727. The valve body is not interchangeable. Not even close.

518's have been installed in A-body cars but it's not for the faint hearted. You better be ready for a major project.