When I installed my SFB, the cutout/welds on the SFB were easy to knock out. The main chamber, on the other hand, was a huge PITA. No way you could just knock it out without damaging the side. Its like they barely stamped the thing.
What I ended up having to do is using my dremmel tool to cut the thing out. Took a little while, but better then bending the side up. I also used a drill to drill out the holes.