Information can be found in the docs in the Developer's Section at http://www.linuxcnc.org/docs, especially at http://linuxcnc.org/docs/devel/html/code/style-guide.html
MH found the following settings in .emacs gives acceptable results (default indentation of 2 characters is unusable):
(setq c-default-style '((other . "gnu"))) (setq c-basic-offset 4)
To match the emc source style: goto c++,code style
define your own code style based on GNU
General settings: Tab policy = mixed, indentation size = 4, Tab size = 8
Please add.