Cobra IRS and Engine differences

Ok I want to take a cobra and set it up for road track and road use. The 1999-2002 are aluminum engine buts not supercharges correct? What kinda boost can you throw at these aluminum engines and what kinda power can you make. I dont think I would want anything over 500. Also what would be the wait saving since the 2003-2004 dont have aluminum blocks? if you had the unsupercharged motor would you go turbo or supercharged? and if so who makes the best for the money for a road car.

Also what are the big differences in the IRS I found this

•2001-02 - mild improvement in axles - 31 spline on the inside while still 28 on the ends. Still has 3.27 gears.

How much work would it take to change the end to take them to 31 spline? sorry I know nothing on this subject. also to change the gears is it much or any different than a solid rear axle?

between the 1999-2004 for what i am wanting what would you guys suggest. I am leaning to like a 2001-2002 because of the aluminum motor the six speed tranny and just upgrade the IRS.

Road course. And they did make 2002 cobra but I guess australia only found out shortly after posting. Coobra r would be my ideal car. But can't afford it so wanna take a cobra to a cobra r level. And I always thought the pre supercharged cobras were six speed. I read today they were not. I can't believe that, thought I knew all mustang.