Compatibility of Optiplex 780 MT motherboard in Optiplex 755 MT???

I have searched the web and the Dell forum and cannot find any reference to replacing a Opti 755 motherboard with a Opti 780 motherboard.

I have a Minitower Optiplex 755 with a Q9400 cpu and max memory of 8 GB of DDR2 RAM which is fast enough for my work, except that it gets bogged down when the memory usage is around 70% or more. I want to install more memory and think that if I can replace the MT 755 mobo with a MT 780 mobo, I'd be able to buy 16GB of DDR3 memory and boost the usable memory to 16GB. I believe both mobo form factors are BTX, so they should fit mechanically. But...I'm not sure it will work.

My questions are the following:

1. Is this feasible at least in principle, mechanically? electrically?
2. If feasible, where can I find a diagram of the headers for each board to know how to hook up the USB, power switch, indicator lights, Audio in and out leads from the 755 case to the 780 mobo?
3. If it is feasible but still chancey, any other suggestions short of buying a Opti 780?
4. Any other suggestions to deal with the high memory usage issue?