Thinking about picking these up for my truck.
http://www.ebay.com/itm/Pioneer-TS-A1675R-300W-TS-A6965R-400W-3-Way-A-Series-Car-Speakers-Package-/400442114397?pt=Car_Speakers&hash=item5d3c35c15d#ht_2489wt_980
I'm sure there are better speakers that I could buy, but these are a good price and I'm just looking for an upgrade over the factory speakers. I know next to nothing about car speakers, but Crutchfield's website says that the 6x9's will fit in the front and that the 6.5's will fit in the rear with minor alterations. What are the minor alterations? Is it just some kind of mounting bracket?

I also might upgrade my factory head unit and possible add an amp sometime in the future. Would I still be able to use these speakers if I did that?