Here is some questions you need to ask yourself:
What kind of oil pressure does it have??. Kind of low??.
What does the oil look like??.
Do you think even if you could get the pan off,you could clean out the engine from a bad bearing let alone check the crank??.
Does it have press fit piston pins or full floating pins.What kind of locks if full floating pins??.
Decide right now the worst and be willing to accept it.
You can run tests like you did pulling plug wires,but at the end of the day sounds like there is something very wrong that needs to come back apart out of the van.Do not run it much anymore.