I fabricated a 3" downpipe using off the shelf circle track exhaust components. Cost under $100, has performed flawlessly for the last 10 yrs.

Start with a turbo outlet flange > 90 degree section > straight 3" pipe > 45 degree section > 3 " header flange. Dont forget to add 2 O2 sensor bungs.

The same tubing can be used for a intake setup.

IIRC, Corky has discussed no more than a 15 degree swage out from the size of the turbine exducer to the size you want for the exhaust. AKA: Start at 2.25, swage to 3, and run 3 to the tip.