Just got off the phone with H&R......The spring set to have is the 29964. This is a little softer in the rear but overall the same rates as the 50404-55 and will sit lower on our E30 318is. It's actually only listed for one application and that is the 84-85 E30 318i. If you happen to find an E30M3 that is changing suspensions then look for 3/1 HA for the rears and 3/1 VA with a white paint mark after it on the fronts. It is the 29664 Kit.
The race springs 50404-88 rates are 315 Front and 570 Rear.
I know I have seen someone post the 29664 is the way to go so whoever that was .....you were right:-)
HTH....
Cheers,
~Ralph