The later A's have more room under the hood and I'm sure the transmission tunnels are a bit larger too to accept the 727's. There may be a "How to" thread out there somewhere.
This is true about more tunnel room on the later A’s. The guy I got the A500’s from used one in his 68 Dart and recently converted to the GM 200 series with an adapter to mate it to his slant. He said he didn’t even bother trying to make it work on his 64 but went right to an 833OD then to a T5!