Exhaust manifolds for an L31 swap from 350?

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I am swapping out the 350 engine I had on my 66 C10 for a new L31 Vortec and the rusty headers are bugging me. I think they will fit the new engine but Im not sure I want to run them. I thought for a start just hook them up and get things running, maybe have them sandblasted and coated. I called around and got a quote for ceramic coating them for $265 a pair. I guess I could wirebrush and use some spray can VHT and let it ride, but Im not writing off stock exhaust manifolds if I knew which to get. I will have a 700r4 trans once I get it all assembled. I dont race the truck just cruising around so unless the gas mileage is improved much with headers I think Id rather have the stock manifolds. Which manifolds are the ones to get? Here is a pic of what the headers looked like on the 350 I pulled.