6x9 all around
Yes they do fit. I have 6x9s in the front doors and rear doors. Like you mention, yes you need to use a spacer or make one. I used 1/4 spacer made from mdf fiber board. Some 6x9s bring spacers too. Depending on the speakers, thickness of the board will vary to clear the magnet. 6x9s rock. I have Polk Audio Momo series. I also have subs for the low end, which hit hard.
1994 Impala SS (One and only original owner)
LT1 383 stroker forged internals / GM aluminum heads / Edlebrock Airgap intake w/ 58mm TB / Arizona S&M cold air and headers / magnaflow cats / Pypes X Violator Exhaust / Yank 3200 w/ trans rebuilt / Eaton posi w/ 3.23 rear........ and others