I'm considering Peerless CSC-X 6.5" woofers for my front doors. They are rather large speakers with a 3.125" (or 79 mm as those crazy danish would say) mounting depth. Using spacers can I clear the outer door panel yet not be so far forward that the stock speaker grill gets in the way?

 

No way, they won't fit. Use 2.85" max.

My type R req'd major cutting with a 1" spacer. Afterwards, it was still a bit tight both behind and in front (using stock grille).