If you only spin one rear tire, you rotate the tire twice and count the revolutions of the driveshaft. If both tires will spin together, then you only rotate them tire once. :thumbsup: Counting the revs is a fairly reliable way to tell what's inside.
The general rule of thumb is that a 2.5L + 4speed manual will have 3.55 gears. But it's no guarantee, especially in 86.