Folks,Had a smoke test done to troubleshoot backfiring when de-accelerating. Sure enough, smoke tests revealed cracks on both original, yet jet coated, exhaust manifold pipes. Question:Best to repair 53 year old originals or replace with todays exhaust products? (I would hate to repair and have cracks occur in other areas of the pipes in the near future). If the recommendation is to replace, what are the forums suggestion to replace a stock 351 Clevelands Exhaust manifolds with and should I replace rears mufflers as well? Thank you in advance! Cliff Folks, Had a smoke test done to troubleshoot backfiring when de-accelerating. Sure enough, smoke tests revealed cracks on both original, yet jet coated, exhaust manifold pipes. Question: Best to repair 53 year old originals or replace with todays exhaust products? (I would hate to repair and have cracks occur in other areas of the pipes in the near future). If the recommendation is to replace, what are the forums suggestion to replace a stock 351 Clevelands Exhaust manifolds with and should I replace rears mufflers as well? Thank you in advance! Cliff