Welcome to the board! I'm a huge Caddy lover myself. I have a '62 Fleetwood 75 Series. I'm in the middle of installing an LQ4 and 4L80E as we speak.
But first and foremost, you have to check out this build thread. Bring some popcorn, it's a thing of beauty. Hands down one of my absolute favorite builds of all time:
https://lateral-g.net/forums/showthread.php4?t=34043
It's a 1957 Caddy Eldorado Brougham being built by a forum member.