I have already mocked up a 42RH/LA block in my 65 Dart wagon. I reworked the upper crossmember including the area where the transmission crossmember bolts up. Had to extensively enlarge the trans tunnel. As I am using what I have laying around, I used a 67-72 transmission crossmember that I modified and reinforced to fit the trans mount and lower crossmember. I am using 66 Dart sests as that what I had available - I think 65 seats would work if they’re not moved all the way forward. FWIW I added a 66 Charger front half console with armrest which does fit between the seats. I am using a 67-72 carpet set as it has a larger tunnel area which does fit quite well. I can dig out pics later
Don