The MOSFET section is rather immaterial....it can be removed from the EK full cover block. The real question is whether the RAM chips line up well enough to contact the EK block's RAM cooling, along with the gpu. If one has to buy separate MOSFET coolers, like Swiftech's or Enzotech's stick-on cooling solutions, so be it. $10-$20 is a heck of a lot cheaper than $90 or more for a completely new block.

Personally, I hope the EK 3870 block will fit well enough on the 4850 card......and am waiting for someone to try.