Good luck with this. In general, you are dealing with a can of worms here and it won't stop until ALL of the paint has been stripped and the full-extent of the rust has been shown to you. We are talking a solid 100+ hours of time to get this right depending on how precise you want to be. I went through this last summer with my 62. Picked out all the old gutter caulk (both top and under the rails, cut out and welded around wheel wells, floor boards. Truck is now at a body shop getting finished up. Had similar rust on the doors, tailgate, lower doors. Its a beast.
But its all doable if you put your mind to it.