I was wrong about the adapter. It mounts to the REAR mount of a 70/ later transmission
BigBlockDart has revamped the site, and not for the better, says some of us. Here's the "old site" tech pages, there's a LOT of great info there on several subjects. You might want to download some of it before it somehow gets lost.
Here's the t hing about the long shaft adapter mount
"here are a few other mods required to use this adapter. The B-body mounting lugs must be ground down to keep the lugs from hitting the trans support rail (Or you can notch the support rail.) (Green arrow.) Also, you will have to give the trans tunnel a couple of dimples with a ball peen so that the adapter attaching bolts don't jam against the tunnel. (Yellow Arrow.)"