Working on the tailpipe tonight. To get the length correct the steel pipe needs to be in the carbon bell mouth the minimum amount. The four holes are approx 69mm apart dividing the circle in 4. Drilling the steel pipe requires a new drill, I used a 1.8mm for the supplied self tapper screws and a wooden dowel I keep that is 40mm in dia is perfect to drill/screw against held in a vice. The screws are cut off after.