Yup, it's possible...
I currently have a '91 YJ tub on my '84 CJ frame. I used the CJ tailgate, so if you didn't know what to look for, you'd never know it was a YJ tub.
There's a writeup on my webpage (link below) and there are some links to others YJ/CJ tubswap pages.
Dan 84 CJ-7
,Weber,HEI. 95 ZJ