Like everything - this a bit like measuring a distance with ELASTIC. It depends.
In plain English - It's a straight swap Plug and Play. A 2008 Classic needs two 5&3/4" units.
But if you have a 2008 Classic without some form of headlight relay - you should do that ANYWAY before the ignition switch craps out.
Q: Is this a swap for the purposes of aesthetics or are you looking for advanced night time illumination?
Why? - You ask.
If the LED units you choose are simple Hi/lo things then you will be reducing load. This is fine for aesthetics.
If you go for state of the art "Adaptive" LED - the load will be just as high in corners. Once you have used these at night, you will shun ANYTHING else.