Can't you just drill holes into the stock tensioner (for tightening it down) to allow it to move more, providing more tension?
Losi should re-introduce this car into the market again as a VTA car, complete with a simple brushless set up. People haven't lost interest yet, I still see them sell on Ebay for a decent amount of cash. Still the easiest car to live with I've ever owned, which is why I won't sell mine.... it is there for the occasional silver can / GT- based racing that goes down locally.