The Civic's stock radiator is an aluminum unit with crimped plastic end tanks.

Normally, unless some idiot does something stupid like lean heavily on an overflow pipe, fiberglass reinforced plastic is pretty tough, and the common causes of leakages would be worn gaskets.

Replacing the tank with a brass replacement or even steel (supposing they can actually weld it without using any exotic alloy) would be a death sentence to your radiator and your aluminum block because of galvanic corrosion. More active metals will make aluminum a sacrificial anode. Though coolants minimize the possibility of this by being a dielectric solution, you can't ignore the possibility.

I suggest just buying an aftermarket replacement radiator, it doesn't cost that much for a brass/copper unit. Unless of course you're weight conscious as the brass/copper unit weighs over twice as much as its Al counterpart.