i used a 2" fernco cap. get em at any plumbing store, or home depot ect. took off the resonator and capped it. you can put the cover back on though, it wont be held on to securely.
here is mine, see how they used to be. the cover is just setting on top, now they have it inlay into the box. the piping is also new.
I used a 2" gripper plug with metal caps and a wingnut to tighten it down. I drilled the bolt where the wingnut fits and added a cotter pin to keep everything snug.
Attached is a picture that gives you a general idea of what the gripper plug looks like. The one that I used had all metal hardware, though. My resonator fit right back over everything just fine.
I believe that the low dyno number (437 hp or therabouts) was due to two things.
Many, many trucks there dynoed a lot lower than they should have. Rhall has a 600+ hp truck, and he only dynoed 10 hp more than I did. There were others with aftermarket turbos, custom tunes and built trannies that were in the 400s. Something was not right, but I do not know what.
I also think that my truck was definitely starving for air. This new intake has made a marked difference in smoke reduction, and I have seen about a 2 mpg increase in fuel economy. More air is helping my engine to run a lot more efficiently.