New to site. G20 Van question.
 

I am trying to figure out how to jack up the rear right side to change a completely flat tire on a 1984 G20 van. I have no idea where to place the jack. I'm not even sure if the jack in the van is the factory jack or not. It has an almost flat plate on top and a J hook on the side. I tried various locations on the back but they all maxed out the jack very quickly.

Can anyone lead me to a site that might help, like a diy site?

I've got no help for you regarding a stock jack, have not had one during my years of owning my G20. I use a hydraulic bottle jack under the axle at the rear, and under the lower control arm at the front. And then place a jack stand in a likely spot, relaxing the jack enough so that it makes contact.

I've had similar situations on some of my vehicles and just got fed up with it.
I got a "Hi-Lift" Jack (about 48" tall) use some adaptors to connect under the Bumpers and pitched the standard jacks in my junk pile in my garage.

As long as you have a place it will fit/store out of the way, I'd go with one of those.

Also...
If you get stuck in mud/etc, the high lift will allow you to pull a wheel totally above grade, and stick a board under your tire.