Is this an appropriate amount of "sliding yoke" visible on an 86 Dodge B250 / A727 Torqueflite transmission?

It looks like it's a bit too far out, however, let me pose a couple of questions:

• Are there any modifications to the truck? (ie: is it lifted)
• Does the driveshaft move at all in the up/down or left right directions?

If the answers to these two questions are "no", I'd suggest you've pretty much don't have much to worry about. The amount which is "clean" (well, cleaner than the rest) is about the travel amount I'd expect in normal usage. This is the area the seal keeps clean by the slight amount of friction and tranny fluid puts on the yoke when in use.