Welcome to the Forum, Andrew. Hopefully, one of our members with a lot of experience on how to open a locked trunk will come along and give you some good advice on how to get that trunk open. In the meantime, you might want to visit the Technical Resource Library (TRL), and take a look at how to do it on a Squarebird. You might be able to do the same thing that others have had to do to get to the lock. Take out the back seat, and with a longggg tool, and the right rachet on the end of it, unbolt the lock mechanism. Here is what to look for in the TRL. 1958-1960 Squarebird Trunk Release Instructions.
The link to the TRL is always part of my signature, and that of John Pizzi - jopizz, who processed your membership application. He is a good man to get to know because he has repaired, and restored so many '58-'66 Tbirds over the years.