76 Cars/What to do about cat converter?

Anybody know what to do about replacing the catalytic converter on a 1976
Cadillac Sedan DeVille 500 cid (owned since new)? There are re-built ones but I
haven't had good luck with them. The new, aftermarket units are a totally
different design, much smaller, and I wonder if they would have a higher noise
level or affect performance. I suspect this same converter is used on Buicks
and Oldsmobiles, and understand Corvettes use it as well.

Any information any one might have would be appreciated.