Weld up the existing slot, finish off with a disk grinder, and place a regular bar with a mount pattern like you want, aligned with the top of the bow bar, and trace the pattern of the regular bar mount onto your bow bar. This will make a low mount bar where you do not need to butcher the cover.
You can mill out the slot on your Bridgeport, oh that's right, you don't have a Bridgeport? So drill holes along the slot and file out with a file.
Make your new oiler hole etc.