I’d like to install an Innovate gauge that includes a wideband and space looks pretty limited to weld a bung between the 3 and 9 o’clock position. I’ve got the Miltek header with cat. Would having an angled spacer between the header and the wideband gauge affect readings?

Your O2 sensor will not read correctly; the wideband needs to sit in the exhaust flow to be accurate. These extensions are usually made to trick the secondary o2 sensor into thinking that a catless header actually has a catalytic converter.