Slant 6 to 340 crossmember question?

I have a 1971 Dart Swinger with a /6 and I am putting a 1970 340/727 in it soon. Are the cross members the same? Maybe just the mounts are different or do I have to buy a new mount from Brewers or Mancini?
And I thought I knew so much about Mopars! Ha, learn something new every minute!
Thanks