Replied by PM yesterday. Here's what I wrote in case anyone else is wondering:You can enlarge the second hole but it makes very little difference to performance and tends to make the mixture a little too rich at part throttle. Also, it's more difficult to get at the rear hole, so overall it is easier and just as effective to enlarge only the middle hole.The Slip-On kit has 122.5 main jets, the MB kit (used for Full Monty) has 127.5 mains and a different needle profile. The MB kit is designed to flow more fuel to work with less restrictive full system exhausts. However, with the appropriate mods to the inlet rubbers and airbox lid, it works very well with the stock headers and a less restrictive end can.Hope this helps. Mike
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.