I've never been a fan of the out the box S/R kits for the reason stated above. Calmini's kit is the worst as it sticks the spring's mounting point WAY down! However those kits are for stock sami springs.
Couple things to consider about using YJs in S/R configuratin:
1) YJ springs are about 9" longer than stock sami front springs. That is why most of your YJ conversion kits use a missing link type shackle up front. If you do S/R you will have to extend the frame out about 4.5"-5" for the tire placement to be correct. More if you want to extend the wheelbase some.
2) With a S/R, like mentioned, when you hit a bump, the axle moves rearward... But that means when you flex it out, the axle will move forward, making it absolutely necessary to have a long travel front driveshaft which is pricey. You could possibly make a square driveshaft for the front cheap, but it all depends on if you can deal with the noise.
I see a definate advantage to using a S/R that is built to maximize approach angle. We wheeled in katemcy a while back with the landcruiser guys. We had 2 zuks, both with YJ springs using Sky Mfg.'S kit. One had 33s and one had 38s. Don't get me wrong it is a great kit, but the springs hang down so far that the zuk with 33s ended up hitting them on everything he tried straight on and by the end of the trip had destroyed one spring AND his tcase as a result. Had he had a S/R that brought the springs up frame level he would have had about an extra 4" of room to work with.
Hope this helps.
