When timing gears are installed with marks aligned on a 351 w is the engine at 1 top dead center?

No, aligning the timing marks on a 351W only ensures the crankshaft is at or very near Top Dead Center (TDC) on the number one cylinder's compression stroke. It doesn't guarantee that the camshaft is also correctly positioned. The camshaft's position relative to the crankshaft is crucial for proper valve timing. The timing marks only align the crankshaft; you must also verify camshaft timing separately.