Will vortec heads off a 96-99 Chevy pickup give more power to 350 Oldsmobile?

No, Vortec heads from a 96-99 Chevy pickup (likely small-block Chevy) will not directly bolt onto a 350 Oldsmobile. They have completely different bolt patterns and deck heights. You'd need extensive machine work (potentially including new intake and exhaust manifolds) to even attempt it, and the cost and effort would far outweigh any potential gains.

Even if you *could* make them fit, the Vortec heads are designed for the small-block Chevy's combustion chamber shape and valve angles. They wouldn't be optimized for the Oldsmobile's design, and might even result in a *loss* of power.

In short, it's not a practical or worthwhile swap. Stick with Oldsmobile-specific heads if you're looking to upgrade your 350 Oldsmobile.