What's best chassis mod?

Right, I get it now about the 6cy torsion bar,
Biggest problem possibly locating one here in uk, but i will try put word out.

Looks like a order from mancinis for the caltracs.

Shop around for best pricing before buying a CalTrac set-up. Complete package will get pretty expensive. I'd like to recommend these guys. Check with Alex or one of the family members for your application. They race Fords, but are good people.
http://moneymakerracing.net/

CalTracs have their own recommended shocks. I like something adjustable up front with regular leaf spring applications. Cheaper ones would be Competition Engineering 3-way. I've had good luck with Koni SPA-1 but am planning to try some QA1 Stocker Stars which have an external extension adjustment which doesn't require shock removal for adjustment. There are better shocks, but I gotta watch my budget too.