I have now successfully mounted almost all the content from DBW/UP to 4.11m + modact, and it works fine ! The only missing things are all the planes.sfs, they work when only mounted but no new plane shows up, when I replace the air.ini with the one from DBW it crashes 60 %. Well like Anto said classfile mods from 4101 work and FM are working when from 409...
But now it is visually almost the same, new cockpits, textures, maps, fbdsm, objects, all 3dfixes, sounds etc

Have also added some other mods :
better pilots, wheelfix, Jcats effects, Uwe's effect + sound compilation, of course ecran wide, FOV mod (default fov doesn't work), clouds big, carrier crew, PAL mini map, battle sounds, Pal cockpit sounds.
All work fine, but some I tried didn't like Gear damage, plutonium, default fov, mission pro combo, hud customize, POV padlock hotkeys and a jet sounds replacement I did for myself (the sounds stayed the old ones).
For now this will be my playground, until I start missing all the mod planes...
Greetings
