Andy, I recall that the Elan Factory did some testing a few years ago and quantified the anti-roll stiffness contribution from the 4 rear drive-shaft donuts. Small but significant I think was the conclusion. (Don't quote me but think in the region of 1/6 the front ARB roll stiffness)
Robin, big bonus of the 2-1/4" ID springs is that off the shelf springs are available at modest cost: not Lotus specific. Ride height can be tuned by an 1" or so to take care of any intended use of the car or indeed spring variation to spec, or sag.
Regards
Gerry
http://www.dfaulknersprings.com/sp225140.htmeg Faulkners can provide the following off the shelf
2.25" (58.5mm) Internal Diameter 14.0 " Free Length Standard Springs
Part Number Description Price Each Ex VAT
14S0060 14" Free Length x 60 lbs ?26.00
14S0080 14" Free Length x 80 lbs ?26.00
14S0100 14" Free Length x 100 lbs ?26.00
14S0120 14" Free Length x 120 lbs ?26.00
14S0130 14" Free Length x 130 lbs ?26.00
14S0140 14" Free Length x 140 lbs ?26.00
14S0150 14" Free Length x 150 lbs ?26.00
14S0160 14" Free Length x 160 lbs ?26.00
14S0170 14" Free Length x 170 lbs ?26.00
14S0185 14" Free Length x 185 lbs ?26.00
14S0200 14" Free Length x 200 lbs ?31.00
14S0225 14" Free Length x 225 lbs ?31.00
14S0250 14" Free Length x 250 lbs ?31.00
14S0275 14" Free Length x 275 lbs ?31.00
14S0300 14" Free Length x 300 lbs ?31.00
14S0325 14" Free Length x 325 lbs ?31.00
14S0350 14" Free Length x 350 lbs ?31.00
14S0375 14" Free Length x 375 lbs ?31.00
14S0400 14" Free Length x 400 lbs ?33.60
14S0425 14" Free Length x 425 lbs ?33.60
14S0450 14" Free Length x 450 lbs ?33.60
I'm sure there's a Australian or NZ spring supplier that can provide equivalents without the UK shipping cost element.