He needs to get the right model transmission for this...
That would be the ball & trunnion type with the rear mount in the right spot.
But other than that, no modifications are required to the crossmember and I'd think that the mount is the same as the original in that model. He can fabricate the extensions to the tunnel fairly easily.
The ratios in that transmission, usually, have the 2.66:1 first gear and he really will need the 3.09:1 first gear, so it might mean he should buy an A-body ball & trunnion transmission and slip the gearset out of it into the B-body unit he uses.
Put him in touch with me and I can help him further.
Ray