Options for 400 BB to 70 Dart /6 kframe

You can get a '73-76 small block k-member and build a Direct Connection k-member OR you can get some big block biscuit mount brackets and build your own. Everything locates from the transmission crossmember.
Yessir! Caint change that, at least , not with extremely expensive excessive fab work.. and I know that is not the goal here