73 nova frame rail

[Mark73]

I have a 1973 nova replacing a frame rail the The shackle bushing hole at the back of the frame rail will not except original style shackle bushings the hole in the new frame rail is smaller than the hole in the original frame any ideas as far as why this would be or what I would need to buy
Thank you

 

[zora]

Where did you get the frame rail and you cannt make the hole larger?