As far as I know there is no standard in gauge 0. In modeltrains the standard started with gauge HO and gauge N.
You can see that in the UK gauge 0 is mostly 1:43,5. In Europ 1:45 and in the US 1:47.
There are differnt kind of couplers. Mostly the manufaturers had/have their own couplers. I have in stock ETS, MERKUR, old Jep and old French Hornby all with differnt styles of couplers. ETS and MERKUR has Märklin typ couplers, ETS coupler, MERKUR couplers and what I call the Bing couplers.
But no drawings I am afraid.
I know old Märklin and the couplers of ETS and MERKUR are compatible.