Need help choosing a junkyard engine

The nice thing about the '67 is that it will bolt in without modifications to the crank. You will have to swap the pan and pickup however but you'd have to do that on the '74 engine too. I'd pop the valve cover and make sure you have valve clearence on all the rockers. If the adjustment is too tight, you can get a low reading. You don't have to do a full valve adjustment but just make sure there is some free play on each valve. Any particular reason you can't fire them up? That can sure help on the valve sealing if they've been sitting for a while.