1979 hobie 16, fitting new mast base question

https://www.thebeachcats.com/gallery2/main.php?g2_view=core.DownloadItem&g2_itemId=133274&g2_serialNumber=3

trailing edge does not fit flush to crossbar, what is the solution? icon_eek
https://www.thebeachcats.com/gallery2/main.php?g2_view=core.DownloadItem&g2_itemId=133280&g2_serialNumber=3

1.) elongate upper hole in cross bar or
2.) notch cross bar for fit or
3.) grind the extra thickness down at back edge of mast step to be like original mast step.

what is the vote??