It may be a little late of an answer, but I looked into this specifically and did it to a small degree of success, but I needed to cut my bottom case to fit the heatsink. I have pictures, but it is on my other laptop so I need to find it and post it up once I do get it. So yes it can be done, but the fins on the heatsink are larger and will stick out the rear some.
I doubt that they can cool to the same degree, the actual fins on the end that the fan blows through has a decent amount more surface area for the fans to cool. I am 99% sure the heatsinks on the P775TM dissipate heat better than the P750 does - even if technically they are rated to hold the same watt hardware. At least that was my experience.