I have used NAPA head gaskets, gaskets that Gunn automotive got for me (FelPro) and Toyota OEM gaskets. All have worked just fine so don't be afraid to use a NAPA part or from somewhere else as long as it is a name brand component.
I seriously doubt your torque wrench is far enough off to cause the problem, but you're welcome to use mine if you think that will help. I have no idea how accurate mine is either but it seems to work OK. Just make sure you are following the correct bolt tightening sequence and that you are doing it in 3 separate rotations like 35 lbs, 65 lbs then 97 lbs.
If you buy a decent quality straight edge from Lowe's or Home Depot in the carpentry tools section it should work fine. Make sure the block deck is really, really clean. Consider using a wire wheel on it to be sure. Once you are certain it is spotless, clean it one more time. I have cleaned blocks before and just before I set the head in place I noticed a small doscoloration. Turned out to be a chunk of old gasket you could scrape off with a razor knife.
Once it's clean, put your striaght edge on corner to corner, down the middle, off to each side, etc. Sometimes it helpful to shine a small flashlight behind it so you can see how much light is coming through. If in doubt use a feeler gauge to determine how warped it is.