The 510 is fixed like a press stud if i remember right so wriggle the tank enough and it will come away with the 510 attached.
If you have already given up on the Alien then take the two screws out you can access and bend the top section up untill you can access the 510 from inside.
If you want to send me it I will take it to work and have someone try before you bin it mate. If unsuccessful I have a TFV12 you can have
You should be able to get two pairs of pliers now and twist them apart then pop that back in the top or the mod