Rebuilding a 74 Duster - Kinda...

I myself would do a mild to serious BB. Fair mileage with plenty of grunt. Easily take care of a 351 no matter how pumped it was built. Easy install with most parts readily available. Nothing like a pull of a Big Block, espicially if money and time are of no matter.
To many head aches with a new Hemi conversion just to make it fit and run compared to an easy BB install. Just my thoughts, enjoy your project and built it your way.