Great looking car, congrats!
I got a 340 that was very stuck freed up with a mix of trans fluid and acetone(I think?) 50/50. I'd try to get it freed up and if it ended up not taking very long I bet you could get it running without disassembly. It took well over a week of soaking the 340 and rocking it back and forth with a breaker bar so there was no making that car run, in fact I had to pull the heads because of the amount of junk that had accumulated atop one of the pistons. But if you got this engine to turn over by hand after only a short period of time, like a day or two, I'd flush it thoroughly and start running some clean oil through it while still rotating by hand, then button her up and try and fire it. You'll either find out why it hasn't been run in so long or you may be pleasantly surprised.
Obviously there will be some red flags that might pop up through the whole process that may tell you why they stopped driving it but if no flags pop up I'd say fire it up!:toothy10: