Here is a link with some info on replacing/location of the flame trap.
https://www.swedishbricks.net/700900F...%20Ventilation

You don't need to replace the flame trap. Just remove it and forget it. Volvo put out several TSBs about the the problem. Flame trap tends to get clogged with oil deposits and most mechanics don't even know it exists.

so then I could just put a catch can in the middle of the flame arrestor hose going to the intake manifold as a sort of back up to the oil seperator, right?

Take out the white flame trap, reassemble the hoses, done. You can add a catch can if you wish. It certainly helps keep the intake manifold clean. I had one on my 240 for a while but I don't on our 960 or 850.