Capacitor

I've found the copper foil in oil caps from companies such as dueland, Jupiter and miflex sound the best, but these can get quite expensive and are quite large

VERY Expensive. I prefer Mundord SESGO or Supreme Silver at just alittle less cash and stunning results. 

Mundorf Mcap,

I've tried Mundorf's lower priced caps, Not even close in perforance to their top of line SESGO and Supreme Silver Oil. Another member here swears by the SESGO, and he is correct, they out perform the Supreme SilverGold. 
Something about the EVO winding tech withina  Supreme casing, makes the superior sonics. 
Not cheap, but well worth it for the nuances. 

Alumen Z are not cheap

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These are the caps Troels Gravensen employs, 
No not cheap at all, , I went with Mundorf SESGO and Supreme Silver Oil.
Which out performed Mundorf's Aluminum caps 
The SESGO are about same price as Zcaps. 

I have no personal experience with trying different caps, inductors and resistors in crossovers.  A local builder of high end speakers that employ compression/horn drivers and wide range cone drivers does not like at all Mundorf and Duelund capacitors.  This is a matter of taste and particular application, so it is not necessarily a comment on the quality of such parts.  But, it does mean that "best" can only be determined by experimentation, with the recognition that any particular swap might not work out for the better. 

That builder will be supplying me with a new crossover for my speakers, but, the parts are quite exotic and hard to come by (Western Electric paper in oil caps).  I hope it works out for the better.

100uf 630VDC could be a safety coupling cap the drivers at 200hz with 8ohm or 400hz 4ohm.
Infinity used to do this to protect their expensive drivers against amps blowing and going DC into them.

Cheers George