Missed this earlier, sorry.
Two options with Ivan's kits and stock headers:
Fit Slip-On kit and keep stock silencer or fit aftermarket end can. The latter will give around 128bhp with no other mods. The stock silencer will give less peak bhp but the midrange gains and smoother throttle response from idle will be the same.
Fit MB kit and aftermarket end can. You will also have to modify the airbox lid, fit a performance air filter and profile the intake stubs. This combination is what is know as the Full Monty. Will give up to 136bhp on a good engine, maybe more if you're lucky.
You should not fit an MB kit without the other mods and certainly not with a stock silencer.
Hope this helps.