340 - Stock Exhaust Manifolds or Headers

I'm ready to drop a rebuilt 340 in my 69 Cuda. I purchased some headers (relatively cheap, $200, NOT tti) with 1/4 flanges. A couple acquaintances recommend I use the stock exhaust manifolds that I have as they suspect the headers will leak and be blowing gaskets. Not to mention the hassle attempting to replace the gaskets by lifting the right side of the engine to remove, replace, etc.
ANY THOUGHTS? Advantages or disadvantages?

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