I have both a 12.5mm drive and the new I-Mod3. Just tried it and you would really have to force the RF shield down and squeeze it hard to get it screwed down. When the RF shield sits on top of the drive there is still 1/8" more to go. So no, it will not fit if you want to put the cover back on and still have a working drive. Most drives have warnings about putting any pressure on the top cover.
As you pointed out, that is an I-Mod2 mounting kit and not the I-Mod3 one. On the I-Mod3 the top surface of the PCB is almost flush with the top of the head sink mounting posts. This is because the PCB also has the 44 pin connector between it and the 44 pin header and so can not go down as far. Buy.com has notebook drives. You can get 10 GB drives for around $120 after $30 discount. You probably won't find a tiny 1 GB drive in the 9.5 mm size.
I skipped the mod3 kit and used industrial strength velcro in two strips on both sides of the VIA controller chip and on the entire bac of the HD.
There is a gap over the chip to keep heat build up down and there is still enough space to bend the ribbon cable over the drive and connect it. Of course the heat sink is removed and replace with the fan.
The metal rf shield keeps just enough contact that it fits perfectly.
I wouldnt do it. Over on ebay, there is one guy selling 4GB 9.5mm Toshiba drives on buy it now for $75. Hard drive outlet regularly sells Fujitsu 9.5mm 4GB drives (on ebay) that go for around $70 (I got one at $70 and one at $60).
These are only marginally more expensive than the one listed in the last post, but are 3x more capacity and 25% thinner.
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