fix overscan on 15khz monitors

[abispac]

Hey thanks for reading, im using recalbox 9.0 with 15khz setting on my rgb moded tv, most games, work out of the box, but some games, like kung fu master, or vigilant, are way to big for the screen. Usually on windows and mame i just create an ini file telling mame to run the game at 320x240, but ima bit confused on how to do this on recalbox.
It seems to be the same principle, create txt file and put it here acordint to the wiki instructions
"All overloads are new files, located in /recalbox/share/system/configs/crt/ directory."
and heres my txt file

kungfum,mame,arcade:224@59.185606,1800,0,0
However that dos not seem to work.
I was wondering if someone can point me on how to force it to display the game at 320x240 or at a resolution that would fit the screen. Thanks for your time.