Tommy, look in most any good outdoors catalog handling firearms accessories, and you will find the synthetic Dragunov-style stock for the Marlin 60. These are described as working with both tube and box magazine versions.
I haven't seen aftermarket barrels. The Marlin barrel isn't easily changed like the Ruger. A good 'smith could probably make a custom barrel, but this would be expensive for a "cheap" rifle like the Marlin.