While getting a set-breakup engine and tender might be cheaper and faster in the long run, another way to go would be to wait until Lionel's service department is back up and running (I don't remember when that is supposed to be since they moved to NC), and maybe even wait until they have a sale on parts, and buy just the "guts" of the TrainSounds tender.
If you go to Lionel's web page and go to the replacement parts section and search "4-4-0", you will get a list of "Generals", just pick one with TrainSounds and click on the "View Parts" button for its tender to get a list of what you need (pretty much everything except the shell and wood load). The down-side to this method is that you will have to assemble and wire it yourself.
Another option would be to get an ERR RailSounds Commander and install it.
Andy