29 mm id is ok if your engine is not going to make more than about 55 to 60 hp.  If your engine is going to make more power than that, you have better get the right amount of restriction on it or your piston will suffer during the long hard pulls.  If the silencer has a spark arrestor it will be severely over-restricted with a 29mm Id silencer core or outlet. 

Why are you not using the silencer that was made for that pipe? 

This is one of the reasons our silencers will not fit any other pipe or other silencers will not fit our pipes.  We have done the testing to get the whole system right.  We do not want our customers shooting themselves in the foot by allowing them put something that they got off of ebay and then blame us for their engine failure or our pipe not making the power it was designed to do.