idk about ROM Manager, but the builds in ROM Toolbox are RevNumbers' builds, and those are designed to run on the GB OTA kernel. If you have the GB leak, it will fail a kernel check on install, so you have to be on the OTA.
I know it has a weird name, but trust me, it's the right file.
Download the file, rename it to update.zip and leave it in the root of your SD card.
Then SBF, do a full reboot (just in case), once it's up and running turn it off, turn it back on holding the x key, then press the search button when the android with the ! appears to get into stock recovery. From there select "install update.zip" and when you reboot you should be on OTA GB.