RE: getting the boom tailpiece off
Some tailpieces have small "shim collars" inside the locking devices that are a bit hard to get out, but I'll bet you have run into the "need to sping the boom" to keep the tailpiece tubes aligned with the boom arm tubes.
Try to spring the rear of the boom arms apart a little as the boom arms are normally the more difficult to spring open as the ends of the tailpiece tubes are a bit wider (when not inserted in the boom arms)
apart than the boom arms.
So, try spreading them out so that the tailpiece tubes can slide out through the lock mechanisms.
What model Chinook boom do you have?
Hope this helps,