Which engine, 4 cyl or V6? What year car?

I would lean to just doing the headgasket. You don't know the history of the used engine either. If yours had good oil pressure, and doesn't burn oil out the exhaust, I would consider it good.

Just an FYI, aluminum heads aren't magnafluxed, they are checked for cracks with penetrant dyes.

__________________
Prost!