No reason why you "can't" but a few reasons why you "shouldn't"

Stock shafts are thin. They will flex during use. They will also "pinch" as you torque them down - this can cause binding of the rockers Also, once pinched the rockers will be a [censored] to get off the shafts. The stock shafts never got a "finish" that would be satisfactory for the full contact of an aftermarket rocker so. as previously mentioned, galling is almost a certainty. Throw them in the trash and spend the $$ on a decent set of shafts.