Rong-zom-pa (RZ1: 157) uses an usual expression go chu rub (within a syntactical structure): “X dang Y go chu rub yin pas ’gal ba med do ||.” Contextually it seems to mean something like: “Because either X or Y would serve the purpose of both, there is no contradiction.” I searched in the TBRC and found a single following instance: dus dang dus ma yin pa dang go chu rub kyi dngos po ston pa (and with some slight variations). I did not study the context but here too, it seems to have the meaning of: “showing X, Y, and Z that would serve the purpose [of both X and Y].” It is just a feeling. Perhaps go here is the same kind of go as in go chod pa, und rub might mean “collectively.” And chu? Simply a variant of chod?
As kindly pointed out by Thierry (see below), the expression is recorded in OTTO (http://otdo.aa.tufs.ac.jp/search/kwic.cgi). As for the orthography cu for chu, we can afford to be quite tolerant for texts of this kind, and simply treat them to be interchangeable without affecting the meaning (e.g. dkon mchog and dkon cog).
Consider the following occurrences (OTTO):
1. rtse rje chungu dang mngan go cu rub ||
2. rtse rje chung ngu dang dgra blon go cu rub ||
3. rtse rje blon dang khrī dpon go cu rub ||
Without venturing to speculate on the individual words, what becomes clear from these instances is the structure: “X dang Y go cu/chu rub” = (probably) “X and Y are mutually representative of each other” or “X and Y are in equal terms.”