how should i repair on my 1996 discovery

 

that is heavily influenced by your location and local automobile emissions regulations

 

The quickest fix (though more expensive) would be to buy a new Y-pipe with new cats. If yours are blocked, not likey theyre any good. Or you could remove them and put in some Test-cats ...if you can get them to fit. Or eliminate the Cat's... but that would be skirting the law -- up to you and the local regulations on that. However, you'll have to figure out how to keep the CEL off (if that matters to you). There are some work-arounds and fixes. But depending on what your time is worth, .....if you figure all the time you're going to spend researching, buying and doing the work-arounds, it almost makes a case for just spending the money and putting on new legit y-pipe with new cats which would be probably no more than 2 hours. Or you can put some black tape over the CEL...lol.

The main thing would be to figure out what plugged the cats and remedy that situation. Excessive oil burings?? Coolant leaks? Bad head gaskets will kill catalytic converters, so you want to make sure all that is good.