That's not a normal Model 70, they are magazine fed bolt actions.
There are exceptions. I have a Single Shot Model 70 in 300 WM, but I built it that way, its my 1000 yard, any rifle any sight/any rifle iron sight match rifle.
Poke your fingers in the mag well and see if you can depress the follower, I bet it's a standard 5 shot magazine.
It it isn't someone did something, which could make it something special or something not so special.
As far if its work $500, hard to say without looking at it. I've paid more and I've paid less. Heck one time I bought 6 Model 70 actions for a total price of $235 for the lot. I've made some damn nice shooters (including the one listed above) out of those actions.
I'd hate to say how many Model 70s I have.
Personally (my opinion only) I think the Model 70 action is the finest bolt action out there.
Here is a fine shooting Single Shot Model 70 in 300 WM