I fitted some 6.5inch Infinity components (605cs) to my Bugeye and made some mdf collars using 22mm mdf, was very straight forward and didn't take long, plenty of room for the magnets and the speakers sounded good. Also fitted some 5.25inch Infinity's in the rear doors, I also added a tiny little subwoofer to it......
It wasn't my fault, I'm from Essex and couldn't help it! Sold the 4-ton sub box when I found out how good trackdays are.
On my Hawkeye I used some Vauxhall Corsa speaker adaptors from a stereo shop to fit some MTX 6.5inch 3-ways as I don't want an amp in this car. You can get the Corsa adaptors from ebay fairly cheaply and they give a fair amount of room for the magnets and are very easy to fit.
Think these were the jobbies...
http://www.ebay.co.uk/itm/Vauxhall-C...item5195753e07
The MTX speakers I've used are a bit of a let down, sound good when turned up pretty loud, but sound really tinny when used at normal volumes, they are powered from the head unit and I think they really need an amp, plus the fact I haven't a clue how to use my headunit properly and the manual is like a phone book
Here's how mine looks........
I also used plenty of sound deadening on both cars, use a heat gun to make it more pliable and follow the contours of the door skins and around the speakers, stops all the rattles if applied well, mine looks a little untidy but I was running out of sound deadening so will have another go when I get some more.
Hope this helps!