Wow! Super cool!

I am thinking that the 1147 number is the patent use number for the Henry rifling as using 1147 as an Alex Henry serial number would put it before this action was submitted for trial.
There were only about 40 of these early bar action falling blocks made and I am unaware of any left side lock versions from reading Kirton and Winfer's books.
This particular example is, imo, a very late one of these bar lock rifles.
Notice how thick the receiver ring is - very much in form like the later back action Henrys. The early bar lock rifles had a very thin receiver ring.
Also, the hammer is much like the style used in the later falling blocks. These hammers are designed to rest upon the top of the action wall which reduces the strike impact on the firing pin. The pictures of the early bar lock rifles in the books don't look like they had adopted this type of hammer yet.
The choice of the 577/450 is strange for a Henry. He must have gritted his teeth with that order...
I wouldn't like any fallingbblock in 577/450 especially an early one like this that would probably have a stepped chamber for the coiled cases, but that said, I wouldn't pass up this rifle if it were in my back yard.
Another sold recently but I don't remember who the auction house was - will have to see if I can figure it out.
Too bad the seller doesn't show pictures of the other stamps and markings. That would clear up a lot.