I put a 72 crossmember on my 70 and the new headers fit fine a little close in the right side but didn't hit anything According to Summit they should fit 67 to 74. These are the ones I bought (
http://www.summitracing.com/parts/SU...UP&prefilter=1 ).
If you can find another 73 measure from the motor mount to the back of the cross member but if your motor mounts bolted up some thing else might be wrong. Check the motor mounts make sure one didn't collapse or soft.
Here are some pix of mine.