SR-71 is right on this one. You won't have the proper connectors. You can try the adapters though. Granted you have enough molex to spare. A new case and PSU would do wonders when you get the chance though. For maybe $100 total for both.
Nvidia recommends a 500W PSU. That's before any overclocking of any sort. On stock voltage, the card alone draws 170W.
http://www.geforce.com/hardware/desktop-gpus/geforce-gtx-760/specifications
I would shop around for a nice PSU in the 500-550W range. They float around the same price range, so just pick up the nicest one you can for the best price. I prefer PSU's manufactured by Seasonic, but there are others out there that are nice.
Once you narrow your search to 500-600W, you are looking for two 6(+2) connectors on the PSU. A Corsair CX 500M can be had for around $40, but I would recommend an XFX 550W for $60. Reason being, XFX PSU's are manufactured by Seasonic, and Seasonic makes most of the better PSU's out there. Good luck. I'm sure you will be happy with that card.
Corsair CX-500M - http://www.newegg.com/Product/Product.aspx?Item=N82E16817139050&nm_mc=AFC-C8Junction&cm_mmc=AFC-C8Junction-_-na-_-na-_-na&cm_sp=&AID=10446076&PID=3938566&SID=
XFX PRO 550 - http://www.newegg.com/Product/Product.aspx?Item=N82E16817207013&nm_mc=AFC-C8Junction&cm_mmc=AFC-C8Junction-_-na-_-na-_-na&cm_sp=&AID=10446076&PID=3938566&SID=
List of PSU manufactures -
http://whirlpool.net.au/wiki/psu_manufacturers