I have the AGI DVD on S&W revolvers and the gunsmith, Ken Brooks, says this about installing the bolt.
He doesn't actually say anything about a 2 piece bolt, he says that some bolts can be installed by compressing the little spring/plunger in the rear of the bolt groove and then just dropping the front into the groove. I can install this 2 piece bolt that way, but not, the normal, 1 piece bolt. For the 1 piece bolt, I need to insert that nose piece into the recoil shield and then drop the rear of the bolt into place. So Ken must be aware of these somehow.
My 15-2 is from 1966 so it's not that old. If I get an answer from The S&W forum, I will post that.