Re-read that article. Nowhere does it say there are two different 27" sizes - there are 27" clincher and 27" tubular, but trying to install a clincher (tire with separate tube) on a rim made for tubulars (tube built into the tire) would not allow you to get anywhere near 15 psi, let alone 80, before the tube pushed its way out of the side.
The chart in that article clearly says that 27 x anything always refers to a wheel with a 630 bsd, ie, same size