Let me ask a few questions cause we got a lot going on here.
If you have a 327 chevy there is no way for exhuast to enter the crank case and blow out the filler cap and damage the timing cover.
Is it a roller motor? If so you need a proper cover and cam button. Do you have a roller cam and no cam button. You may have other problems if so.
How much gas did you put in the engine like a shot glass full or more than that? More can cause hydro lock since you cant compress a liquid it will break a piston or stretch the head bolts and blown the head gasket. Or all three of those things. I got a feeling you problems are a lot bigger than a bent timing cover. Which is fine with normal cam just smack it back with a hammer. But that is not the problem. You have a broken piston or at least a blown head gasket.
I hope this helps. Sorry to hear things arent going well.