I would recommend ditching both sets of heads and finding a set of large valve heads in the 72-75 cc range.
Why spend the same amount of money on a small valve pair of heads when you can sell off what you do not want and build a large valve pair
The 350 would be as expensive to build as a 400...possibly more due to piston limitations.
IMO, build the 400 with 72-75 cc heads and be done. The HP ratings based on block code are determined by cam and heads. You can take a 200 HP block, rebuild it with a 068 cam and #16 large valve heads (not to be mistaken with the 1970's) and get a net rating of 330 (generalizing).
Si Vis Pacem Parabellum
1967 Starlight black PMD Engineering 400 Auto 1968 Alpine Blue 400 4 speed 1968 Verdoro Green 400 HO 4 speed 2013 1LE 2SS/RS Inferno Orange Camaro.
