If there's no aluminum in the cooling system (water pump, thermostat housing), leave the brass in the shop and use steel...
Brass is much higher on the galvanic scale and will kill aluminum components.
A good example of this is the PRV V6 shared by Peugeot (the designers), Renault and Volvo. In the Volvo, and only in the Volvo, there's a brass plug in the block to drain the coolant. The block is aluminum, as are the heads and everything else (very neat light engine).
The Peugeot has very little problem with corrosion, but Volvo blocks are usually badly eaten out. I've known people who've had to change engines because of water leaks out of the block.
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