In either late 1954 or early 1955, Savage changed the receivers on their Model 99 to accommodate the slightly longer .308 Winchester. The next year, Savage added the .243 and .358 Winchester cartridges to the calibers available on the Model 99 as well.
I agree with Clodbuster that you'd be far better off to buy a "99" chambered in .308 rather than .300 Savage... and have that rifle rebarreled to .358 Winchester.
BTW, $485 for that rifle is an excellent buy if the rifle is at least 90% or better condition. You should "jump" on that one ASAP. :-)
Strength & Honor...
Ron T.