No YJ will not fit. IIRC the samurai is 37 front, 39 rear, 2" wide. YJ is 46/46 and 2.5" wide.
Again, IIRC, post 76 CJ rears were 2.5" wide and about the same length, maybe with an offset centre pin, but the fronts were only 42" long and 2" wide! A near perfect match.
So you can move your samurai rears to the front and put CJ fronts in your rear without the hassle of new spring pads, etc because everything is the same width. However because they're longer you'll need a folding shackle. This combo was pretty common in the past, but CJ springs aren't floating around waiting for people to haul them away for free as much as they were. CJs fronts are easy to order if you're in a hurry.
There are indeed a lot of companies out there that sell kits that allow you to put the wide YJ springs in your samurai, but adding 9" of leaf length to your front isn't trivial. And has the big downside that your samurai gains 'fangs' in the front which like to bite into the terrain in front of you that you want to climb up...
I don't think YJs really get anything over the much simpler and cheaper rear/front/CJ/folding combo and they involve a lot more work, at which point I'd say call Kevin at Kore4x4 and enquire about doing a full proper coil conversion instead.