Rich,
On the FRST you need to drill and tap the inlet plenum 1/8" BSP (as close as possible to the standard ACT sensor for the ECU so that the gauge is seeing what the ECU is seeing) to get the "factory fit" look. You can then screw in the elbow and either blank this off OR fit a vacuum pipe to this for a boost gauge. You MUST do one or the other, or it will be leaking air from the elbow.

Hope this helps and sorry for the confusion, you obviously got sent the instructions for an RST.
Best regards