This thought comes to mind. If you can get the chain back up, just secure it. With the mechanical advantage the cam and valve setup has, it is likely that rotrating the cam is in fact opening the valves and the valve is pushing the piston down. However, you will never be able to push a valve closed with the top of a piston, so rotating the cam leads you to believe that's not the problem. Lets simplify this situation. Don't drop the pan. Do what Steve suggested, remove the rocker stands. This will disable the valve train and all valves will remain shut. Get a good purchase on that chain and see if you can get it to come around. If you say you've got all of it out then the only other thing could be piston valve contact. See if you can get 360 degrees of crank rotation. If you can, get #1 at TDC for compression and get the cam back in synch with the crank. You really only have two possible scenarios, Donnie's and the one Steve and I described.
2000 Dodge Grand Caravan SE