94 Disco "knocking" noise

94 Disco is making a "knocking" sound & has lost a major amount of power. Floored it gets to 30...bad right? What the hell is it? Took it to a muffler shop, they listened & said it might and might not be the catalytic converter...land rover manual says it should be replaced if you hear a knocking sound. Anyone dealt with or heard of this before? Please let me know what this is...definitely hurts to see my baby just sit in the driveway. Thanks

A knocking with a huge loss of power does sound like the cats, it's too bad it's such an expensive part on LR's what with the dual cats on the same pipe and all. You might want to check a junkyard, they'll usually do stuff like that for fairly cheap.
Good luck with it

I found one at an auto parts store for $79...will it matter which brand or will it do the same purpose no matter what?

You want to make sure it's a reputable brand, cause if you put one on that is more restrictive than stock (stock is fairly un-restrictive) then you will lose power. But, that might be worth it because a stock one is so dang expensive. Just make sure it is a decent one and that it looks to be about the same size as the stock one.

Let us know how it turns out.