I have discovered this ONLY with RTB and BL mods 1.6a.
So, the idea is, that you go to data, go to missions, copy the level data and paste it to rtb/blmods 1.6a data.
It's so bloody cool, so do it yourself!
ATTENTION: Only some of the levels work in each other mod. Maybe there are only 2 maps what works in each other. The maps i have currently discovered:
Missions to rtb:
-Mountain colony - DEATHMATCH
-Bedroom slopes/rampsV3
-buildbox 1.2
Mission to Blockland mods 1.6a:
-Lavapit update
I'll bring here the news for other levels, as soon i find it works.