I also ended up destroying what was left of my sub when I took it out, and the holes did not fit my new sub. I have two suggestions for installing the new sub in the old enclosure if you haven't yet:
Use
speed nuts to make the new mounts more secure. I just rotated my new one a little bit and drilled all new holes.
Stuff the enclosure with polyfill/batting to deaden the backwave. Batting is the fluffy white material that goes inside pillows or stuffed animals and is a couple of dollars per bag anywhere that sells fabric (incl. walmart). Tease it with your hands to loosen it up, and aim for 50-75% fill.