Update: For those who don't want to mess with Heimdall and swapping kernels to get root on stock UCLB3, I've put together an Odin tar.md5 that will install the AT&T / Samsung 2.3.6 Gingerbread release with root already installed. This will install just like the Samsung leaks, and comes with all of the same stuff: stock kernel, etc. After I finish testing and uploading it, I'll start a thread in Development.
This will eliminate having to go through a long list of difficult steps to get root on stock UCLB3.
EDIT - I have a working tar.md5 for this, but need to work on it a little more before I post later this weekend.