The 85-88 columns are the same. I think the 84 is different internally, as it relates to the turnsignal and cruise control stalk circuitry. The one from the 85GT will work. I don't remember if yours has cruise, but if it doesn't, you can use a column from a cruise equipped car. You can get a complete set of key cylinders for the ignition and doors, but the trunk cylinder isn't available any more. It would be best to have the trunk cylinder re-keyed to match any replacement door cylinders you install. Maybe the cars you're looking at have the keys and cylinders you need.
When I tested your trunk lock, the key I found inside would turn the cylinder, so that must be the correct key. The trunk latch was in the locked position. You may try turning the key and inserting something into the latch to try to unlatch it, but until you're absolutely sure the lock is going to work, I wouldn't lock the trunk, especially since you don't have a remote release.