SS springs

Questions between the SS and XHD springs for a 1973 Dart Sport.
1) whichs ones are stiffer?
2) which ones make the car sit higher?
3) when you talk of pinion angle you mean degrees below horizontal. Correct?

I just bought this car and it had the SS springs on it but I thought they were shot because it sat s o lows in the back so I ordered and installed the XHD springs. When I changed the springs I found that the front spring mounts were flipped. So there is probably nothing wrong with my SS springs.
Which ones are recommended and why? I have a 8-3/4" diff & don't know what it's from.
Sorry, don't mean to hijack.