Tranny men please read my torquenverter

The flex plate will only go on one way. Very possible the bolt heads are too thick. Should be obvious if you have the correct ones. You might have not had the converter fully seated. That will kill your trans. When assembling the trans to the engine, you should have had to pull the converter towards the engine a small amount when putting the converter bolts back in. You better drop the oil pan, and check the thrust bearing. It's probably destroyed, and will throw shavings all through the engine.