Hi, welcome! The rust shouldn't be to much to repair, provided theirs not a lot more in places you can't see but I've seen some members here work miracles. Your's doesn't look bad at all. The door panels can be restored but I would say the dash pad will have to be replaced but there not so expensive. You have a nice starting point that truck looks good and it belonged to you're grand father, cool. Don't get in a hurry don't lose you're vision and find a place out of the weather to park it.
