I recommend replacing all pre and post cat gaskets with OEM from www.sewellparts.com
if replacing out o2s...... double gaskets if your metal has deteriorated rapidly cuz of aging. Seal up any air leaks for a better o2 reading. If there's ANY air leaks (assuming your cats are good still), that'll interfere with o2 readings and might bring up same cold. Stay POSITIVELY optimistic! You'll get it done bro!