If I were doing this I would get rid of software serial altogether and make the two Arduinos communicate via their hardware asynchronous ports.
You need to think laterally and use that stuff between your ears more.
You need to research and learn about software serial library and its limitations and to know that it can not and will not do full duplex as your topic title states.
When you write:
Wiring: Same as the figure on Gammon forum, resistors connected on arduino 1 side.
Again, you are making a total assumption that everyone knows what and where to find that figure. I would guess that only 1 out of every 1000 people here on this forum would know what you are talking about, maybe even less. So, I hope my point is made clear by now, provide links and concise information.
Paul - VK7KPA