Graphics Card Replacement / Conversion Options?

I have an iMac (Late 2006 24-inch) with the nVidia GeForce 7300GT graphics card. It has had three graphics cards fitted over the course of its life. Now, the GeForce 7300GT has failed once again, and frankly, I'm a little tired of a lousy GPU ruining what is otherwise a good machine.

I have been studying the ATI Radeon HD 2400XT from the 20-inch Mid 2007 and Early 2008 Aluminium models and noted a few key points:

• The card confirms to the MXM specifications, sharing the same connector edge with the 7300GT, including location of data and power lines
• The physical shape of the card, including screw points, heatsink mounts and component locations are identical to the 7300GT
• The iMac 24-inch power supply maximum output is higher than the 20-inch power supply, and therefore should satisfy any power requirements
• Physical component and socket layout of the system is not the same, but similar enough. Air flow paths and blower locations are the same
• Both models are EFI32 systems
• The output resolution to the internal display is the same, the card is not required to push any more pixels in normal use
• Mac OS X should load the correct kernel extension without any software modification

Some things I haven't been able to confirm for sure, mainly because I won't know until I can get my hands on the card to test:

• Whether Apple changed the firmware between models to the point that the older iMac would reject the newer card
• Whether the system bus speed change between 667MHz (24-inch, 7300GT) and 800MHz (20-inch, 2400XT) has any effect on the MXM cards ability to function

In theory, the Radeon HD 2400XT card should be able to slot in place of the GeForce 7300GT, physically fit into the computer (albeit maybe with some modification to the heat pipe routing, or reuse the 7300GTs heat pipe) and power up without any issue. I expect that provided the logic board and firmware accepts the new card, the LCD should also function as normal as the card delivers the video signal back to the Logic Board via pins outlined in the MXM standard and the logic board handles the control of the LCD panel itself.

Now, this is quite a costly exercise. The cheapest Radeon 2400XT I have seen for sale is a used card from a Mid 2007 iMac, for $199 plus shipping, so it's worth doing as much research as possible to minimise the chance of it not working when installed.

Can anyone confirm that this should be doable or provide information as to reasons it won't work? Are there any details I have overlooked that I should be researching into first?

Thanks in advance.