64 Dart Project, need help please

Should be fine - my car is a 66 w/ automatic trans and there is an oem rubber pad that sits above the trans on the torsion bar crossmember. Its screwed into the crossmember, from below if I remember correctly. Anyway, the trans tail shaft sits very close to it. I assume your car is similar. You are probably okay. The rear of the trans doesn't move much anyway.