475V is such a pain - its just too much for the normal 450V rating.

Best I can suggest is 2 off Panasonic ED Series 220uF/250V in series (with voltage share resistors across them).
These things are 18mm diam and 40mm high so two of them will take up 36mm just under the 38mm = 1/5".

The ED series are 105 degrees C rated and are Low Z Hi Ripple Current jobs.

If you can accommodate Solder Tag connection then get JJ Electronics type TE050 100uF/500V. These are 25mm (1") diam and 42 mm high.
They are only rated to about 70 degrees C however so placement (not too close to your tubes) is fairly critical.