yes the mcw30 is compatible with 2 cards in sli, at least it looks like it is because it's much smaller than the maze 4 and it does say on their site FULLY compatible, makes quite a point of it.
There are other blocks I believe but they were aimed at the sli dr so they are ultra ultra low profile and look like flow restrictors to me, also why would you want anything other than swiftech? I love their stuff, the only thing that stopped me having their gfx blocks was that they were push fit but I think they've addressed that now too.
And dude, if you can't get a water kit in a V1000 you shouldn't try, a) it's loads bigger than what I have 2 loops in and b) it'd look daft with a radbox underneath.
Get decent tubing r603 tygon, danger den clearflex or xspc like I have and the turns you can pull off are amazing.
Also if you think.. bayres, small pump and a 120.2 or pa160 rad installed in the case (cut a hole in the top of it for a 120.2 easily) and all the blocks on the motherboard, what exactly is going to be easier using a radbox?
Any help you need just shout, there's loads of people on here will help you. An awesome PC spec like you have deserves awesome cooling