Using that rad whether you tap it out or not, it's a dead rad. Bin it and buy a new one. It might seem over cautious but water will find a way out of if there's a even a tiny imperfection, and inside a pc case with the hardware you have, that's a lot of money down the drain. just words of wisdom from someone who has gone home soaking wet more than once, and it wasn't always just water.
where are you mounting the rad so the ports come out the front. My original idea for this case was the same as yours. a 360mm rad in the front of the case, i've still got the bracket i was going to use. From my measurements, sitting the rad central in the case meant that the port end of the rad would stick out slightly out of the side of the case, all of the rads I could find in the UK.