Overdrive in Early A

Distance from the face of the bellhousing to the center of the transmission mount is 14" on the 904 in my car. I've found dimensions online for the 42rh of 15 7/8", so 1 7/8" towards the rear of the car. So, as others have done, just modify and enlarge the existing crossmember + tunnel work. The same dimension on the 200-4r is 26 7/8", so 12 7/8" farther back. While the 200-4r is shorter and smaller, it may not be worth the substantial crossmember modification (or entirely new crossmember) vs the 42rh.