In around 1980 S&W strengthened the model 29 because silhouette shooters and hunters using heavier bullets were wearing their guns out prematurely. The strengthened guns have some refinements in heat treating, and also have the heavy underlug that you see on today's 629s. If you stick with 240 grain bulllets, you'll be OK for a lot of shooting if you have the older model. You may hear or read that S&W 44s are not as strong as Ruger 44s, and this is the origin of the story. As you can see from the date of refinement, it hasn't been an issue in over a quarter century.
Another issue is whether you need to have it tapped for scope mounting. New models are tapped for scope mount with the holes being under the rear sight. I don't believe this feature was added until the 1990s. So you may need to have a gunsmith to tap it for you if you plan on scoping it.
The 1970s were a dark age for S&W and there were some guns of inferior quality made then. I'm not sure how to tell whether your prospective gun is one of these. They weren't horrible, but they were a low point in S&W quality.
So there are the potential negatives. In general, though, the 29s have a history of being great hunting guns. Kind of like getting a custom built gun for a true bargain price. It's the 44 against which all others are judged.
