I have read all the door speaker threads, seems most are replacing with 6.5" splits. This was my plan but I have come across some JBL 8" 3way 2 ohm 94db co-axels that are tempting. Not sure if they would fit though. Anyone able to confirm if they will/won't fit with a 6mm MDF spacer to replace the factory speaker/plastic moulding?

If you really wanted to you could modify the doorskin so the speaker sits on top of it but getting it to not rattle will be a challenge. There is very little chance you would get a 8" speaker inside the door without cutting away at metal. Personally wouldn't bother trying to fit anything larger than 6.75".

Any after market speakers (in a 380) will need a MDF spacer or some kind of custom mounting system up front.

You will need custom kick panels to fit an 8 inch driver in the front doors.

Unless you are building a top shelf, audiophile system, 8 inch drivers in the front aren't needed IMO (and the fact that you're looking at coaxials for the front suggests you're not after an audiophile system).

Stick with a good set of 6.5 inch splits with sufficient amp power.

Thanks, thats what i figured. Will stick with decent quality splits in 6.5". If it would have been an easy I might have been tempted with the lower freq response of the 8".

8 inch front coaxials are neither here nor there for bass frequencies.

Only a subwoofer can do that job effectively.