I am thinking about doing some exhaust work on my 300 I6. I have had a few ideas, but are afraid to persue for a couple reasons. I know that most exhaust systems are tuned for the engine, and that poses the main problem. Right now I am running stock system, slightly modified (cut exhaust short, no muffler, dumps under bed, 3 1/2"x12" chrome echo tip). Dont get me wrong that alone made it sound fairly decent. But the other problem I ran up against is the catalytic converters. They have never been replaced in the 17-18 years it has existed (1989 F-150). I dont really know if they are clogged up or not, so I'm not sure if it would be worth it to do anything with them. They do rattle though, mainly when I pump the gas, or running about 15mph. I imagine that rattle is because of the burnt up catalyst 'pellets' in there. I have thought about removing them, but that will make it hard to keep it street legal (not a licensed farm truck). But, on the other hand, I dont have the $250+ to replace them. If I do end up taking them off, what exactly is to be expected from the engine? An increase/decrease in power? Or increase/decrrease in gas mileage? And also if I persue any route at all, what would be a good pipe diameter to use? Something that will echo, be some-what loud, but withought sacraficing compression. Cost?

Any advice is appreciated, Thanks.
-mlow90