Yes..you should be able to. You'll have to take off the starter, remove the front engine mount to be able to lift the engine slightly then remove the oil pan.
No. Crank and main bearings can be get at by dropping the oil pan, but to get to the small end rod bearings you've got to get the pistons out.
Just remove pan and change bearings.
I don't believe you can because the oil pan on vans are double sump pans and there wouldn't be anyway to get the pan out of the way because of the crossmember.
Sometimes it's possible to change the big end bearings by pulling the sump off. But to get to the small end you need to get the pistons out. And if you're pulling the sump, and the head(s) you might as well get the motor out first as it'll probably be faster.
Yes, you do not have to remove the engine.
No
If you are talking about the crankshaft rod bearings, you can just remove the oil pan, and replace each crank bearing one at a time without actually removing the pistons. But to replace the piston pin rod bearings the pistons will have to be removed. IMO, if any of these bearings are worn bad enough to need replacing, then the engine needs a complete overhaul.
the ign switch or the key & tumbler ???
I assume you mean to ask how difficult it is to change the main bearings WITHOUT pulling the engine out of the vehicle. Don't bother. To properly replace the main bearings you need to pull the crankshaft away from the engine far enough to be able to put a micrometer on the bearing surfaces of the crankshaft. To do that you need to disconnect the crankshaft from the transmission AND pull the pistons part way out. Also, depending on the type of seal used, many rear main seals must be replaced by pressing them into place after the crankshaft is in. Don't even try to replace bearings without first verifying the status of the crankshaft. It must be round and within tolerance. If the old bearings have worn there isn't much chance that the crankshaft hasn't been affected.
open up the rear axle differntial drain oil locate the bearings and take large needlenose pliers and gently pull the bearings out without damaging the differncial housing (expensive!!!!!!!!!!)
In most engines, yes only if the crank is not damaged and measures correctly.
In some cars, you can get the rear bearing by dropping the transmission. For the rest, no.