I'd drill through the base and screw them on from below, it allows you to rotate them so the rail holes are in line.
As for making use round bar, cross drill for rails first and then turn from that, mill if I want any squares where the rails go or at base, saw/part off, face bottom end true and then drill and tap for fixing.
Edited By JasonB on 31/07/2020 12:08:56