The XE engine exists in two formats, most easily recognised by differences in the belt train or by reference to the engine number (up to 14142838/from 14142839). A less apparent difference between the engines is in the valve spring platforms.
On the later engines the valve spring platforms were redesigned as a shallow ‘top hat’ shape, which gives more positive positioning for the standard valve springs. The improved support and positioning make these later platforms the best option for an engine using standard valve springs.
However for an engine using race quality double springs, a flat valve spring platform (as found in the earlier engines) is required, since the raised section at the centre of the later platforms makes it impossible to fit the inner spring used in a race spring pack.