If you get brass hose barbs that have a 1/2" npt, the inside diameter of the threaded end is 5/8". Just hacksaw off the bulging ends of the tubes on the heatercore, deburr and clean them, and slip them on with flux, then solder away. JBWeld would work fine too.
I used this on my current setup (soldered).
If you want it purty, you can dremel or file the threads down, and make the fittings look custom.
And Quaky, if it's a heatercore style radiator, it's gonna work fine. Just about any heatercore will outperform the black ice radiators, but they just won't look as nice, and are a tad bit larger.