1971 Ambassador Compartment Door Pop Locks

[SamWind]

I purchased two replacement compartment door pop locks from Vintage Trailer Supply for my 1971 Ambassador a couple of months ago. They're beautiful, but I've run into a problem with removing the old lock. I can't figure out how to completely remove it. I removed the operating part of the lock, but I can't get the shell of the old lock off. The base of the T-part remains on the outside of the panel, and the cylinder that contained the operating part remains on the inside. It will twist back and forth (limited by the trim piece on the door). The T-part on the outside and the cylinder part on the inside are two different pieces that are connected in a way I can't figure out. On the cylinder part on the inside there's a I guess I will call it a tang looking thing, that suggests if it were depressed in some way it might cause the two parts to release. The new locks look the same but they're different than the old lock in that the T-section on the outside and the cylinder on the inside are a single piece. With the old lock, the compartment door is sandwiched between the outer T part and the inner cylinder that used to contain the lock mechanism.

Please tell me how to take this thing apart.

TIA
Sam McKerall