It looks to me like you have an ex-military '98 action that has been fitted with a model 54 barrel. I am a bit confused about the serial number on the triggerguard, as the triggerguard should be from the '98 mauser, not the model 54. Maybe it was re-stamped??
I'm not sure if Winchester made a manlicher stock for their model 54, I'm guessing not. Probably aftermarket.
All in all, I think you have a very fine rifle, assuming the barrel was fitted properly. To do this, the shank had to be cut and rethreaded. One nice thing, is that if you want to attach a scope, there is no collector interest in your combination, a simple drill and tap for top mounted scope, and a low-profile safety, and you're set!!
For the price, you did very well, indeed!! I have a similar rifle, bought from a private party who brought it back from Alaska. It's a Czeck VZ24 action with a pre-64 7X57 barrel, which I'm sure brings collectors to their knee's, weeping. It was in the original Model 70 stock, which had to be butchered to fit the '98 action, so I had it restocked.
Let us know what the gunsmith says!
Enjoy!!
Mark