Not in my case, BitspowerDD Fatboy ½" fittings and 3/4" OD Tube...wow, i'd be tight with 3/8" ID tubing even...I doubt it. If the fittings were in the center of the block versus on the bottom edge or top edge it could be done.
I think there is no water block that will allow you to have 3 Double-Slot graphic cards right? I just checked PPCs and none of them have the connections on the sides so you could water cool the SB.

With the Mosfets, NB and SB on WC, my NB sits at 21º-22ºC and SB at 19º-20ºC in BIOS, I don't have Everest yet to check them under load.
Those are good temps. Are you using 1 pump for all that?