seen it done pretty simple
take some flat stock cut a hole same size your hedder flange is take your tube tap in the sides enuff to get to fit in the square hole slide tube into the square drice a tappered wedge (pyrmid) inside the tube
makes a perfict fit
least to the jig you made

1970 barracuda convert. 1 of 59
1970 pro street A.A.R. clone (panther pink)
1971 charger
2015 hellcat challenger. Redline red
2014 quad cab 4x4 ram 8 speed hemi