Looks like the other A pillar is full of bondo. My guess is its covering up more rust holes. Judging by the floor and rockers, I'd bet there's more rust covered up by bondo, any work done before it got to you would have to be suspect.
Looks like a lot of good parts to be had though. I'd still part the poor thing out unless you just happen upon a complete set of A-pillars so you can weld them in above and below the pillar. That's the problem with getting a car that's been worked on, you never know what the other guy did, or covered up. There can be a lot of hidden problems underneath the paint/primer.