Having restored a few of these - I can see several spots that if they are rusted, there is more hiding. The good news - is that advancements have been made in replacement panels for Blazers so you can get fixed it a LOT easier now than you could even 2-3 years ago.
Congrats on the new truck. I have been looking for sheet metal in that same Medium Green color for my 71 blazer project. You have all the panels I need!
Welcome to the Blazer family. Keep posting pictures as you dig into it - there is always help on this forum and plenty of really informed people on these rigs.