[Arran]

Mike;
  The ones they used in these Canadian G.E KL-500s are even smaller then that, maybe 3/4 of an inch across, and 1-1/2 inches tall. I'm sure something may fit, but how long they will last I don't know, would a modern 22uf at 350 vdc be able to take the ripple? Believe it or not I think Bob here has the early production KL-500, those had the P.M dynamic speakers, and a resistor between the two filter caps, the later production ones used a field coil speaker, probably because alnico 5 magnets used strategic metals like nickel, not sure about the cobalt, it's a 1941-42 model.
Regards
Arran