are there 2 versions of the 340? I got a challenger which was originally a 318. a previous owner somewhere down the line put in a 340. I got some stuff to dress up the engine a bit, but there are some problems. first is the mopar valve covers they will not snug down...they hit the manifold. second purchase was the march pulley system. It needs a spacer almost 2 inches at the alternator to get everything to line up. March is baffled why it will not fit right and so is the place where I got the covers.
any thoughts?

 

Nope...if someone milled the deck and the heads it would cause your valve cover issue. Try using some of those thick old cork type gaskets. Your problem up front may be due to what year water pump you are running and if the have matching pulleys. Water pumps and timing covers changed in 1970. Post some pictures of your issues if you can.