Reproduction Frame rail installation

We've finally got to installing the driver's side frame rail on my 70 Challenger. I bought a Sherman frame rail thinking that it would be better than the off brand torsion bar crossmember I bought but it was made by the same company "CHL". Either way the frame rail is isn't sliding into place. It's about 1/8th of an inch of and I was wondering if anyone has any tips on how to get it all the way in.

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Author: bullet18