I installed 4 - 4" Infinity Reference speakers in my Westy about 18
months ago. The rear installation was very easy. Just unscrew,
disconnect, and install. For the front doors, as mentioned above, I
used a Dremel rotary saw tool to saw off the threaded part of the
stock speaker covers. I reinstalled the stock covers over the new
speakers with four black finish screws for each speaker. In the door,
the speaker cover must be flat because the window crank arms pass over
them. So discard the covers that come with the new speakers for the
doors. I found this solution well-documented in the archives. It
certainly worked well for me.

As for the sound, the 4" Infinity Reference speakers are an
improvement over the 17 yo stock speakers; however an
amplifier/subwoofer really gives you the greatest stereo improvement.
Even so, I don't really enjoy the stereo while freewqy driving because
of the high noise level inside the van. While parked or on back roads,
however, it's a very good-sounding system.