I toyed around with the X1/9 rear spring/strut swap. My problems were the fact that the Yugo mounts were two bolt vs a three bolt pattern on X1/9 mounts. Additionally the rear struts are not designed to turn, fronts are and have a plate made up of pin roller bearings between the spring seat and the top mount to reduce the effort to turn and reduce wear on components. My best solution was to use Lancia Scorpion rear springs with stock Yugo struts and mounts. Gave about a two plus inches drop and a very nice firm ride. Off the struts Yugo sprigs are about 5-6 inches taller than Scorpion springs which are a couple inches taller than X1/9 springs front or rear. X springs are not tall enough to have any contact if your car is in full sag. The stock Scorpion springs need an inch or two of compression to assemble the strut so even if you were airborne the springs stay in place. I put Euro springs on my Scorpion so I just happened to have the old ones and X1/9 springs lying around the day I decided to attempt to lower my Yugo. A few years later I am still very pleased with this modification. Take a look at my Svetlana photo album to see the new control arm bushing I had made to replace the rubber ones... Really firms up steering response and improves tracking and acceleration.