JBA short-tube headers do not have a cat or mid-pipe. Long-tube headers of any brand should mate directly up to existing or aftermarket cat-back exhausts. JBA also produce a set of high-flow cats with attached mid-pipes, which fills the gap between the end of the shorties and your exhaust. Looking on High-Horse Performance, the cost of a set of JBA shorties + high-flow cats with mid pipes works out to be the same as a full long-tube header.
The main cost of the $600 mid pipes are the catalyctic converters, which are chockers full of platinum. Overall I recommend getting the high-flow cats and mid-pipes to go with your headers. Otherwise, I *think* the stock cats are built into the mid-pipe anyway. Sorry if that was a bit of a roundabout way to answer your question.
