Unfortunately I'm using eZ 3.7.3 and it seems that there are too many features not available in this version and required by my patch (thinking about ezclusterfilehandler for example).
I understand I will have to upgrade to eZ 3.8 first. Am I right ?
Yes then you need to updgrade to latest 3.8.x. This is well explained in documentation. http://ez.no/doc/ez_publish/technical_manual/3_8/installation/upgrading/upgrading_from_3_6_x_3_7_x_to_3_8_0