M6500 modify nvidia 2800/3800m heatsink to fit Radeon HD 5870?

Hello, looking to migrate from M6300 to M6500, I use Manjaro Linux OS. I want the ATI FirePro M7820 gpu but am unsure about what it means that the Radeon HD 5870 is the same.

There is a steady stream of m6500's coming through Ebay/craigslist, some quite cheap, but most have an nvidia card. I found the following post which states that some metal was cut on the nvidia heatsink and the ATI fit right in. However, this was on an M6400. But, I read any m6400/m6500 cards can be swapped. Anyone else do the same modifying the m6500 nvidia heatsink for an m7820, any ideas?
http://forum.notebookreview.com/thr...ers-lounge-part-2.425226/page-62#post-8627083

I gather the Radeon HD 5870 is the same board as the ati m7820, and seem to be somewhat available. Are the 2 boards actually the same, one can be swapped for the other?
thanks

 

The M6500 does not use MXM, it is non standard, as such the best card for it is the Quadro 5000M? or similar, I forget exactly what.
However, the M6600 is fully MXM standard.