When I done the firs mod I was asking one of my friend (he build amplifiers), what should I do to get the best results from the filter capacitors. He suggested me to build similar what I have done. The more balanced steps you have between the biggest and the smallest cap is the better in theory, to achieve an ideal capacitor.
I had 5cm X 7cm boards for the 4 electrolytes in the Third Mod, and more caps need wider board of course. You just need to measure the diameter of the capacitors to see the minimum you need. Minimum means all the caps fit, but it not means if you put the hex spacer to the corners you get a good location on the PCB to drill holes, so bigger board give you more freedom to pick the right spots, then you can find the optimal arrangement for the capacitors. Prototyping boards breaking easy after a cut on the surface and sandpaper can take care of the rough edges. The Elna For Audio you have is perfect, the film capacitors are superior compared to electrolytes for audio purpose in general, but size and capacity is problematic. As I see beyond 1uF the electrolytes are easier to use. In theory the same brand and series are better because the similarity of the internal materials and dielectric, in practice you get different sound by mixing brands or series.
No point to stick to K73-16, if you have easier access known brand MKT capacitors.
