I fitted a two speed 16" fan to my 450 but it didn't fit inside the existing shroud. It's possible the shroud is a different shape on the 500 and you might be ok, with local temperatures here it rarely runs at its high speed so can't say how it will perform for you.
I definitely noticed an increase in power and reduction in noise and hopefully the repeated slight increase in temp before the fan switches on doesn't do any long term harm compare to the mechanical fan.

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1973 450 SLC
2001 Volvo V70 T5
2010 Aixam Mega eCity