the do make a piece of pipe that looks like a cat on the outside and is a straight pipe on the inside, just buy a cone filter from the autoparts store and put it on the end of the TB thatll work just as good. i wouldnt go with a 3.5" thats a little small 3.6" is pushing it as is with headers. as for the canned tune id try to find someone local who can tune first as a in car tune will always be 10000X better then a canned one