The ITA's done some awesome work digging up the original route. There's also a modern-day trail called the Three Blazes, but it follows a very different route - over toward Chamberlain Basin, well east of where the original Three Blazes went. And, unlike most of the trails in the Frank, it's decently-well maintained!
I'd also recommend Merciless Eden by Doug Tims, who (along with his wife Phyllis) own the Campbells Ferry homestead. It's also a great stop-in if you're running the Main Salmon - hike a hundred yards up the hill, ring the little bell, and they'll give you a fascinating tour of the place.