How can I find the gear ratio in a chrysler 8.25 w/o a tag and w/o removing the cover or driveshaft

One kind of cheap way to do it is to safely raise the rear of the vehicle, & then put it in neutral, so that the tires r able to spin. Get under the vehicle. Mark a spot on the tire as a reference, to where u want that reference to start & stop on the body of the vehicle or something. Also mark a spot on the end of the driveshaft, & a reference mark to have a start & stop as well. When u r ready, then rotate the driveshaft in either direction, & count the rotations it makes to one rotation of the tire. Then that would be ur rough guess gear ratio. Hope that made sense.

Turn the tires and count driveshaft rotations. It is pretty basic stuff.