Vladek - with my 2005 4/4 I did get about a 10% increase in performance on the dyno, and very noticeable improvement while driving. I didn't find any real improvement in economy - but was already getting about 40mpg and I haven't really been trying to drive it economically! I had already fitted a K&N panel air filter in the original air filter box, before the exhaust system was fitted, and that also had a small but definite effect on performance. It is difficult to find an aftermarket air inlet system that will fit in the Morgan, and it is important to ensure it draws in cold air.
I don't know if you can use your existing cat, it may depend on the engine/model. On mine the cat was part of the original highly restricted manifold so it was all replaced.
