Hi Swizzyman ,
For $103.52 before shipping (the cost of the linked transformer) , I'd git my butt to one of these swap meets the guys are always talking about and buy up a whole trunk full of radios to take a transformer out of . On a cost VS value basis nothing would beat grabbing some swap meet radios , just make sure some have a 5Y3 in em and you'll be all set , that 350 0 350 , 6V , 5V transformer has gotta be the most common one used in parallel wired sets .
And then think about all the nice leftover parts you'll have to go into other projects . In the grand scheme of things , does a 78 year old radio really NEED a brand new transformer when used = pennies VS dollars ?