Now this is the conversation I wanted. I need some more parts to do m21 install which at earliest would be next year. Also plan to do myself. Car originally was four speed so some of the parts are still in there

As far as running the 3.90 one change would be great if running those gears is an option. As far as the factory 400turbo matched with 3.90 being built stronger keep in mind that would have been I behind 350+ horsepower so with my weaker motor maybe the trans will hold up a year or two with the 3.90 and if I install right I don't have to do it again