3 to 8 weeks, depending on how back logged they are and how far you are from their shop. I would recommend you call or write to them with your frame serial number, they'll tell you availability of the barrels you want and if they can fit them to your frame. The 450 Marlin barrel is an asterisked* caliber which means it can't be fit to all frames and I'm sure the 500S&W will be too when it becomes available.
phone (978) 630-8220
email hr1871@hr1871.com