Captain slow, when it starts playing up, does it settle after it cools down? To me, it sounds like what our previous 406 v6 did. It would intermittently lose power, miss and stall. Would run fine after few hours. Turned out to be a dud coil. Try and see if you can borrow a coil from someone on the forum or get a second hand one for testing purposes.
It has 3 catalysts - a small pre-catalyst bolted onto each manifold and then a main one. The catalysts on the manifold are not especially large or heavy, so freight will not be as bad as you expect and an outfit like Interparcel.com could be useful. The main catalyst can be easily replaced by a generic one of the appropriate size, but spend a little extra and you get a stainless case. Expect it to sounds a little different. The oxygen sensors are relatively inexpensive, so you might even start there.