so ill keep this simple. no, a 8" speaker will not sound good if you just simply cut the metal to make it fit and mount it. it takes a good amount of sound deadening becuase the 8 will vibrate a good amount destroying the sound quality. best way to mount an 8 to the door is fiberglassing. a nice set of 6.5 components in the doors with the tweets either in the a pillar or the door near the mid would sound great for a daily setup. if you want 8s put them in the kickpanels but that still takes fiberglassing.
hn155: Rockford punch pro speakers, t400.4 deh 80prs, full audio build to come. working towards 175hp n/a, simple but fun.