Brammer: If you use the turbine housing that comes with the turbo, you need to extend the downpipe a little and convert it to v-band. If its a internally gated housing in OE cosworth spec. from atp turbo i dont think the downpipe needs modifications, but do not know for sure.

The spacer is needed when going external gate, OR if the compressor housing is A/R .70.
If it is A/R .60 it will just clear the manifold without spacer.

The GT3071 and GT3076 both comes with .60 or .70 compressor housings and with or without antisurge. It depends on the serial number and what year they are produced in.