Looking at some early 1990s ATR catalogs, I agree with Neal. The sections and welds on the pipe match up and the wastegate/control valve looks like ATR. Should be 304 stainless, so non-magnetic. Old pics show the wastegate had "APPLIED TECHNOLOGIES" printed in red around the perimeter of the top. maybe there is some outline of that printing remaining.
downpipe part# DP301
ATR had a billet wastegate part # WG100D and control valve CV100A
can't find a part # for the cast wastegate pictured.