My '97 Mazda 626 2.0 4cyl overheated and won't start. Is it the head gasket...?

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It turns over and continually sounds like it is about to start but won't. A "master mechanic" looked at it and said it's a blown head gasket. I already started removing the cylinder head to replace the head gasket, but did not do a compression test first. I have not seen any oil/antifreeze mixture, but the car has been putting out white smoke for months intermittently. The spark plugs, battery, distributor cap, router, spark plug wires, coil, coil wire are all replaced. Suggestions?