I put an 72 cross member in my 62. The upper two holes on each side of the cross member L-bracket are the ones I used to properly locate the cross member to the 62 frame. You show these holes in your second photo. I then had to drill new holes, or slot existing ones, for the rest of the bolts. A 63 cross member should attach the same way.
Also keep in mind that the large bolt holes coming up through the bottom of the frame are spaced evenly front to back 63 and later vs the 62, shown in this thread -
http://67-72chevytrucks.com/vboard/s...d.php?t=703583, post number 9. On the 62 the rear hole is closer to the center hole.