I'll sell you my front,rear swaybars and springs from my MCS for $200.

 

Rollin- If you are not chasing the perfect H Stock setup, go with aftermarket springs. If memory serves, the stcok SS+ springs were close to $300 for that you can buy any aftermaret spring available.
SS+ and stock MCS F&R sway bars are the same part number.
For H Stock shocks and the front sway are free i.e. you can run any brand or size.
I left my stock front bar (thinner less understeer) changed shocks, rear sway, with a MCS stock bar, and ordered the correct factory SS+ springs. There are 6 differnt part numbers for springs on the Cooper and three different part numbers for the MCS. The spring and its rate are determined by the options on your car. To find out the part number go to your dealer and have them run your VIN and options to get the correct part numbers for the springs. In addition the ratio of rates is different from MCS to Cooper, based on the extra weight of the supercharger.
A legal SS+ Cooper needs the following changes from non-SS+: rear sway (MCS stock) and SS+ springs.

 

My mistake - I thought SS+ included different springs.
FWD-MX5, would aftermarket springs be within the rules for in H stock?

 

No, front sway bar and shocks are the only free suspension mods for stock class.