There should be another bolt under the engine cradle where the pipe mounts to the frame. There is usually a silent block (a tubular piece of rubber with bolts coming out of each end). Connect one side to the frame, and the other to the mount on the pipe (usually on the expansion chamber).
You parts look like they just gave you a bolt that goes through the rubber tube. This will work, but it's not as nice as a silent block. You can order one from treats later if you like.

The third connector will be to support the silencer. The silencer will also have a long stinger attached to it that goes down the center of the of the subframe connecting to the loop that goes through the swing arm. You'll need to remove the pillion seat to get to the silencer support mount. there is probably a hoop that goes around the silencer. That will connect to the bolt with the tab welded onto it. The hole in the tab will sit between, or on the side of the hoop mounts depending on its sizing, and the bolt will go up into the mount on the subframe.
This pipe doesn't employ a gasket. It has a bevel that fits up against the reverse bevel on the cylinder. It's good to employ some copper gasket sealer on the two of them because they can leak. Loosely fit the two bolts on the cylinder until you get the other two mounts loosely in place. Then tighten up the two bolts at the cylinder, and then the engine cradle, and then the silencer. This sequence will ensure proper adjustments where needed. Also use some copper gasket sealer at the joint where the stinger attached to the loop.
If you check out my DRP thread you'll find photos of how all of this goes together.
With regards to the restrictor in the pipe. If you have a rotary tool just use it to grind the weld down to the point that you can remove the restrictor. Then use the rotary tool, or a round/half round file to clean up the pipe.
