stock springs w/ aftermarket springs ??
 

Can I leave the stock springs in the rear and install RB springs in the front ?

Thanks

NO! you're messing with the car's handling that way. The springs will have different rate of compression. There is a reason the spring kits comes in a set.

If you like to lower the fronts more than the back then go for Teins springs, they lower the front around 1.5 inches and the back around 1 inch. I got Eibachs and surprisingly got more drop on the front than the back. There is still slightly bigger fender gap in the front but is less than before. ;)

Why would you want to do this anyway?