All Ruger Americans are not the same, re: magazines.
https://ruger.com/products/americanR...ets/26974.html
This particular predator model (listed above by StraitR) uses AI pattern magazines with 3/5/10 round poly mags available from Ruger, and 5/10 round ones from Magpul. It's 18" barrel is also threaded from the factory at 5/8-24. Ruger's muzzle brake for the GSR will also fit in place of a can, if you so desire. The compact stock can be purchased from Ruger. assuming magazine compatibility is not an issue. I assume the existing stock could be cut down as well.
http://shopruger.com/Muzzle-Brake-30...uctinfo/90602/
http://shopruger.com/Ruger-American-...uctinfo/90537/
I doubt you will find a better deal than that!