I'm far from an expert but I have a little experience with turkeys. Glad to hear that he "gobbled" up the food. I would probably give the aspirin every 4 hours - 6 hours for a few days. He will tell you if he is still hurting.
Just re-read one of your post and you said you have a BBB. That is a fast growing breed. BBBs are born to be eaten in 4 - 6 months. You have a true meat bird. That will probably explain everything. His legs may be giving out on him. He is a "table" bird. Sorry. :/
What were your intentions when you got this turkey? Pet? It's similar to that of a Cornish meat bird. They are born to be eaten within a few months. Some can live to be longer but the odds are very slim.
But if he were not a table bird, this is how I would answer your post.
It doesn't sound like Mereck's.
http://pubs.ext.vt.edu/2902/2902-1098/2902-1098.html
Do you have any feral cats or rat infestation in your area (outside, woods, etc?) Where did he come from when he appeared injured? Do you have predators that could have fought with him and injured him? This baffles me.
Don't worry about the poop pic. In fact, I'm glad that it was included.

Seeing good poop is good. And that was a question that I was going to ask.
What does the bottom of his feet look like? What about his hocks? Be careful with him always on his elbows. They will swell very bad and that will be the next problem. I know this sounds crazy but can you rig up some kind of cushion for his elbows?
I just think his time is limited. Sorry.