Head on collision of two black holes
Well the spin is easy. Your system has zero angular momentum, so the spin will be zero. 

I think there will also be no gravitational radiation. for the slightly technical reason that gravitational waves only come from changes to the quadrupole moment of a system and in your system the quadrupole moment is always zero. 

So everything ends up in the final black hole which will have mass about 4.6 billion solar masses, coming from the mass of the two colliding holes, and their kinetic energy.

I'm not sure exactly how long the merger would last, but it will be comparable to the Schwarzschild radii involved, divided by $c$, so around three hours (as seen by a distant observer).