How do you know when it's time to replace it?  The reason I'm asking is the master cylinder is off (and of course the engine is out) so it's right there with easy access, but I'm not sure it needs to be replaced.  The "rag" part of it looks really good and I did not feel any play in the column last time I drove it.  I did do some research from old threads on this site (lots of good info) and I was warned to stay away from the parts house aftermarket jobs due to poor quality.  So it would have to be either original GM or one of the restoration parts suppliers.  I am curious, however, about the "repair kits" that some of the suppliers offer.  Looks like they're just new bolts and new flexible material, but not the steel parts.  Way cheaper.  Are they worth messing around with?  

The parts house "repair" kits are best left for emergency use only, imho.  If your joint looks ok, and you see/feel no play in it, it's prolly ok, but...as you say, it's right there, and you've got lots of room to do it now. I think I would go ahead and replace it, and have the original for a spare, in case ya need it down the road.
Good rag joints are a bit pricey....for a reason. They last longer, and are not as flimsy as the aftermarket "one-size-fits-all" jobs.
my $.002

you probably know this but just in case... if you change the rag joint... remember to have your steering wheel lined up the way you want it...  before you put the halves  together...

Thanks, guys!

The part that fails is always the rubber "rag" part of the coupler. The metal component(flange) never has a problem. While I have used the "repair" kits, the quality from one to another is spotty at best.

If you really look at the coupler, you'll see that the shoulder bolts("locking pins") are really what does the actual turning work(especially on manual steering cars)...the rubber part is flexible enough that it will allow the pins to contact the mating slots in the gearbox flange, and turn the gearbox. The rubber is there to help with reducing any vibrations going to the steering wheel, and to allow for any slight mis-match in the alignment of the gearbox and the column.
 If the rubber coupling fails, or gets weak, that's when you get play in the steering. If there is enough play, after a while the flange and the pins will wear, giving you even more play in the steering. The "repair kit" rubber that I have seen might be really good, or really crappy...ya just never know what you're gonna get. I've gotten some that I wouldn't use on a go cart, and some that were well enough made to use on a Mack truck...it's just a crap shoot. I've also seen some that were not thick enough, and would rip apart in about a week.
If you want to try the repair kit deal, I would suggest making sure the replacement rubber is at least as thick as your original, and that you cannot bend/flex it very easily by hand...it should be pretty dang sturdy. Also, the really good ones will have the outer edge of the rubber completely enclosed...as in, you cannot see the plys of the nylon used to strengthen the part...like the belts of a tire....if that makes any sense. In the pic of the one in your link, you can actually see the nylon string/thread on the flat surface of the part....

Thanks, Joel!  Good info on the repair kits.  I did notice that Zip has what appears to be a more robust repair kit that mimics OEM more closely (also costs twice as much as the one I linked to) but I think I'm just going to hold off for now and keep an eye on any excess play.  Or I may decide to get crazy later this winter and buy a whole new OEM ass'y.