Tired of header leaks , will these manifolds fit a

I'm going crazy with the headers/ manifold choice . Heard good things about dougs , but to fit them is harder than manifolds , taking a sawzall to the headers in there now , hooker SS super comps .
Motor tested 390 hp 413 lbs torque with headers , how much would be lost with manifolds ? If under 20 hp it's worth never having a leak and going manifolds .
Have 5 months of storage t decide .
And 412 Stroker the car is a complete resto , numbers matching show winner , but will be driven , orig motor is in storage , manifolds would make it 100% they were the only thing not original