An interconnection assembly for a motherboard uses right-angle edge connectors attached to a bottom side of the motherboard, and vertical header connectors attached to the top side. The header connectors mate with a transition card assembly which includes a transition card having plated through holes that receive pins of the header connectors. Right-angle mezzanine connectors mounted on the transition card have pins that extend into the plated through holes from the top side. The edge connectors and mezzanine connectors both face forward in a common direction. The transition card has holes along a rear edge to retain pressed-in nuts for mounting to a stabilizing bezel. Instead of pins being part of the header connectors, connector caps may be provided with pins having first ends that extend into sockets of the header connectors and second ends that extend into the plated through holes of the transition card.