Every once in a while the shifter would jam when putting it in reverse. Lately, it's doing it every other time time I drive the car. I did a search, but couldn't find anything specific. It's not hard to "un-jam" it: just reach under the car and make the rear most lever vertical. You don't even need a pliers to do this. Has anybody else had this prob? Would a rebuild of the linkages solve this(like just r/r the rods). Or is it an"inside the casing"(rebuild) job? Thanks...

Try adjusting the rods first, sometimes the play needs to be adjusted to get it out of the jamming spot.

Try adjusting the shifter levers first, and make sure all of the linkages are in good condition...not sloppy in the lever holes.
If that doesn't do the trick, the problem is most likely the shifter itself...(this problem is not indicative of anything amiss inside the trans.)
The shifter can wear, and allow the levers to slide past the gates, leaving the trans in a gear, while the shifter is in neutral or another gear, which locks the trans into two gears at the same time.

Check out the photo link below for how to adjust the linkage. (Ignore the "Install bolt here" notation...that was for something else). The factory GM shifter will of course look different than the Hurst, but the idea is the same(the alignment hole for the factory shifter is at the top, I think). Insert a drill bit/pin into the alignment hole, with the trans in neutral. Adjust the linkages for the shifter so that they all fit nicely into the shift levers on the trans.
hth

                                               Click image for link

   Took apart the center console and checked out the shifter. Looks like you have to take off the side of the center console to put a pin or "locking gauge" (as they call it in the manuals) in it. I'll have to do this later... Thanks for the input.

Upon further review... It looks like my shifter is shot. So I'll be replacing it instead of adjusting the linkages. Anybody ever replace just the shifter..?

Many a shifter has been replaced.  But you can rebuild it as well, and use the original parts in the car.  It's not always possible, but it's also not difficult to acomplish.

UPDATE: I had the shifter rebuilt, and that took care of the problem. Linkages really didn't have to be adjusted...  Shifting is a little tighter when going from a forward gear into reverse. Forward shifting is good in that there is less "slop" between gears. As always, thanks to all who responded... 

Well, I'm glad ya got it fixed. Too bad it wasn't just an adjustment, but I was afraid it was going to be a worn out shifter issue. The thin gate shims in between the selectors wear, and let the selectors just kinda hang wherever they want to be instead of where they should be.
Oh well...at least ya got it going again, and you shouldn't have that problem again for another 25-30 years!

...."another 25 to 30 years"...  I agree! It's just hard for me to see how these metal parts(which were lubed) could wear out so in a car that gets pretty good treatment.