Q:

Questions regarding Falcon Heavy's crossfeed system

My understanding of the Falcon Heavy cross feed system is that the outer cores feed six of the nine engines directly on the center core.  Thus, the cross feeds don't pump propellent and oxidizer into the center core tanks but rather feed six of the nine center core engines directly.
This is very similar to how the Space Shuttle worked.  The Shuttle's cross feed between the External Tank and the Orbiter was 17" in diameter -- one for propellent, one for oxidizer.  A project to reduce the size of the cross feed to 14" was cancelled.  A video of the disconnect being tested can be seen here: 

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Some questions:
How large are the cross feeds between the Falcon Heavy's outer cores and the inner core?
Are there four (2 for propellent, 2 for oxidizers)?
Has cross-feeding been done on any other vehicles other than the Shuttle and the Falcon Heavy?
Do the pumps reside on the center core?

A:

Cross-feeding has been used (sort of) on the early versions of Atlas: these had booster engines that were fed from the first stage tanks. These engines were jettisoned while the first stage was still running. Of course this is a simpler construction than the proposed design for Falcon Heavy.
The Space Shuttle also isn't really comparable: the SSME's are fed only from the ET, there is no switchover to another tank.  
This will be the critical point for Falcon Heavy: they need to switch the engines on the center core from one set of tanks to the other, without interrupting the flow of oxygen and propellant. High-speed turbopumps are sensitive to flow issues, and inserting a gas bubble into the liquid flow could be disastrous.  
Also, when you close a valve in a high-speed flow of liquid, it's difficult to avoid creating a fluid hammer (a pressure spike traveling upstream from the valve). 

A:

There is an image floating around, I do not recall where I got, called the LOXtopus, which is the manifold at the bottom of the tank showing the plumbing. 

There are a total of ten connections.  Nine are for the nine engines hosted locally.  The tenth is for draining/filling.

