late model torsion bar crossmember into early A body

The front frame rails on your 63 are closer together than the 67-72. The ends of the t-bar crossmember go all the way to the inside face of the rockers. A new crossmember can be modified (shortened) to fit but the centerline distance of the large female hex t-bar sockets are different between the two generations. 24.46 vs. 23.0
So that's a problem that's not easily fixed.

Look in the parts car section here or post a wanted ad. Maybe someone will cut a solid one out of a parts car for you.