Here is the AT&T 4.4 Kit Kat with Sense 5.5 RUU version 4.18.502.7
It has radio version 4T.24.3218.09 and will work with this config:
File name is:
RUU M7 UL K44 SENSE55 MR Cingular US 4.18.502.7 R10 Radio 4T.24.3218.09 10.26.1718.01L Release 356565 Signed 2
You should not need to downgrade your hboot version for this RUU to work. This should work for most S-On users that need to return to stock since there a lot are on a software/hardware versions lower than it.
If you need support for using this file you can use this XDA thread:
The full list of RUU files can be found here: