You might want to consider building your car to the SCCA CSP regulations. This would allow you to also race autocross (many more of those around than rally cross), and then just throw on some tires for rally cross. Adjustable shocks like Illuminas would be about the only must have item to swap between the two genres.
www.re-speed.com will have just about everything you need suspension wise which ever direction you decide to go in. Plus plenty of advice. Great guys to deal with.
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