[Arran]

I saw a few Stromberg speakers on fleabay, whilst looking up info on your model 60, I don't know if the diameter and electrical characteristics were correct however, and the prices on some were somewhat less then realistic. My guess is that the diameter of the speaker in the 60 is similar to the 128H, an 8'' one, but maybe they stuff a 10'' in there to make use of the push pull #42s? In any event one will turn up sooner or later, either in a junker console or at a swap meet, if all else fails see if you can find one that needs the chamois replaced on the outer edge, that will bring the price down.
The capacitor can shouldn't be too bad to restuff, the modern poly film caps are much smaller then the old paper ones, and the terminal board on the base gives you something to mount one end to. What you need is something to fill the empty space inside the can, what I once did with one in a Canadian Westinghouse set was to take one of the original paper caps, and layed it on it's side in the inside top of the can, and then filled the can with a combination of candle wax and tar I salvaged from the can. You could also try gluing some strips of Masonite or thin plywood on the inside of the can to give the terminal board some support and go without the wax or tar.
Regards
Arran