Nothing to be gained removing the tube and barrel from the receiver, I'd leave them alone. For that matter, it wouldn't hurt to leave the compression chamber in place, if it is stuck that tight.
This manual says the pump lever is the same as the 140, therefore the 1400 will work, it just won't look right. Are you trying to remove the compression chamber with the trigger still in place, or have you removed the trigger?
If the seal between the valve halves is tight, you won't lose stored air. It will make pumping very inefficient, to say the least.Got to be a reason why it won't come out. I wonder if it's hung up on the threads? Hung up as in larger than. Maybe the only way to get it out is to remove the tube.