For the record, most rads are copper and have brass solder/brazing- most fittings are brass and then plated. All high-quality watercooling components should be aluminum free, so just make sure you check if ever thinking of using components that seem sketchy...or just avoid. Thermaltake was guilty of having aluminum tubed rads as well as components with aluminum fittings (TT Bigwater components, for instance). Zalman also likes to use anodized aluminum in their gear as well.
But it's still an issue, so you can't just work under this assumption. However, this has more to do with radiators and fittings than actual blocks- blocks typically aren't the issue, unless it has to do with integrated fittings or components ON the blocks. Almost always, it has to do with fittings, couplers or radiator components that are aluminum.