I understand your needs as I'm no audiophile either. Now beer-ophile, that I am
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Anyhow, so you're looking to fill out the sound with stock door "tuned ports"? In that case, I'd save yourself the time and more importantly $$$$ and just mount your new door panels w/ nothing behind them. You'll get the same effect. I'm not saying that to be a smart a$$, I mean it in all sincerety.
Do a search in the archives here, on ppbb.com or on renntech and you'll see what I mean. Every 6 months or so, someone w/ a 986 will post "help - my door speakers don't work". Those of us who have been around will them to turn up the radio really loud and put your hand next to it - you'll feel some slight vibrations/air movement - that's it. The poster will then come back and say, yeah I guess they are working, but they really suck/seem useless/etc. Reason being, the OEM amp has a filter built in that only sends low end freqs to the doors. With 5.25" speakers, you can only get so low and are therefore only getting (in my est) about 5-10% of the possible freq from them.
However, if you are seriously bent on installing the OEM tuned ports, I'd only pay $10 ($20 MAX!) for a set (including shipping). When I ripped mine out, I thought hey, I'll put 'em on ebay. Checked it out and 6 other people had the same thoughts as me. Most of the auctions ended w/ no bidders - even w/ opening reserves of only $9.99. So in the end, I left them sit in the garage for a week and then just pitched 'em.
JM2C
Good luck!