If you have a corrosion inhibitor you can mix copper and aluminum, but I don't know how well it would work or for how long. It would likely be easier to get a standalone radiator.
It would also be easier to get a copper/brass radiator than it would be to find an aluminum water block, but if you have to get a different radiator you may as well get a separate pump.
The Bigwater 760 isn't very good for WCing anyways. It needs a free 5 1/2" bay above and below it for airflow, for a total of 4 bays. A better option would be a pair of single 120mm radiators like the MCR120, which are the best bang for the buck in the US/Canada, or a Thermochill PA120.1 which is a solid performer at any level. Mount them on the top and back exhaust fans, with the fans against the case sides. I'm assuming they will fit, you'll have to check the sizes, as I don't have your case myself.
If you have the modding skills, using one dual fan radiator like the MCR220 or the PA120.2 will be slightly better, and may look cleaner, but requires that the top or back of the case be modified.
Pump wise I would recommend a Liang DDC (aka. Swiftech MCP350) or a Liang D5 (aka. Swiftech MCP655). Both of these pumps run better with an after-market top, like the EK Blocks EK-D5 X-TOP. It made my pump far quieter. The DDC is reported to be 25dBa or so, and can be undervolted from 12v to 9v safely. The D5 uses 1/2" fittings natively, the DDC uses 3/8". Both cost the same.
I wouldn't recommend a reservoir. A T-line does the same basic job and can do it better. If you want one though, go ahead. I use one and have no problems, but if I did it again I'd go for a T-line. It's mostly about looks here, go with what you want.
Distilled water is the best and easiest coolant, so long as all of the components are of similar materials. (
Read Here for things that work together and things that don't) Primochill tubing is a good choice, and isn't too expensive.
MCR120 $35 x2 $70
DDC and D5 {with speed control} $75 for either
Bitspower fittings (Plain Janes) $6 a pair x2 $12
Primochill Tube is about ~$20 for 10'
About $177 + Taxes
If you use one dual 120mm radiator you save about $20 + $6 for fittings.
It should also allow you to cool the CPU without trouble for an extra ~$50