[redrooster]

I recently swapped a YJ frame under my CJ, so here's the deal on going the other way.
First and foremost, the YJ frame is 4" or so wider in the front than a CJ. This means your motor mounts won't work, and neither will the spring mounts on the axles. You would have to fab mm's and move the springs outward.
Next is that only 6 of the 8 tub mounts line up and the grill support doesn't line up either.
I haven't checked out the crossmember, but since the YJ had a different trans and t-case (driver drop) it is doubtful it would work.
My opinion, get a new YJ frame or weld and plate the crack you have. If the crack in the pics is the only one, then I would say repair it.
I got a YJ frame in good shape from Palmer Brothers in Birmingham, AL for $300. They had several. It would save you a lot of time and hassle to replace like for like. A shackle reversal is easy enough to do on your own after the swap.