If you are using a 67 and newer trans there is the problem,the crossmember mounts on the frame are a little longer on the 67 and newer that will allow the crossmember to go back a little farther then the 65 and 66s. I installed a 390 and a 67 C-6 in my 65 country squire and I made two plates to move the crossmember back a little. Back in 79 when I installed a 69 390 and C-6 in a 65 galaxie I ran into the same problem but had no clue on what was wrong and modified the mounts,I heard rumors about a 66 crossmember made for a C-6 that will work but have never seen one. What I done in my wagon was mount the motor and mount the crosmember to the trans and measure the distance from the holes and made two plates with two holes to bolt the crossmember in,its a little hokey but it works and you will have to take up some space in the E brake adjuster as it loosens it up with the crosmember moved back. Jeff