Maybe but I can't say for sure unless your cpu is stock clocked. Is your 260 the 55nm or the 65nm version? If you do go SLI make sure the psu isn't getting hot and you will be using two 4pin molex to 6pin pcie power adapters. As for the board can I fan mod.
My CPU is stock clocked. my current gtx 260 is 65nm i have previously ran this video card with 600watt no name power supply that had 12v current of 26amps and it had no PCI-e connectors so i had to use two converters for it. and my point is, that with that PSU, it ran perfectly fine no problem. SO Iam guessing it will run fine with SLI on this PSU but still im not completely sure. Anyone else know anything? plz let me know!
It would be tight, it has two 25 Amp rails.... mmm It might work just fine tho.
IMO, sell your gtx 260 and buy something new, like a GTX 460
Hope this helps