I've had the front spring hangar moved into the sub frames on four different cars, first was a 1963 Plymouth Belevedere that we center the Mopar kit like the instruction said to do, the third one was on my1971pump gas Duster that I had the boxes moved all the way into the sub frames so the outer edge of the new boxes where welded against the outer frame rail to get as much additional clearances as I could on that car. The second car I ahd done was 1969 Dart and I had the inner edge of the boxes welded into the inner edge of the stock sub frames to get clearances between the stock gas tank and the leaf springs on the passenger side, I still had to dent the gas tank for additional clearances
The last one was on my 1966 Dodge Coronet and I helped a friend, a pipe line welder move those boxes all the way in also after denting the new gas tank for spring clearances on the passenger side