I think he should make his decision regardless of weight. At 240, you really shouldn't have to take any special considerations. You should be able to ride any frame without problem.
+1 on checking how much repairs it needs. If all you need is a minor tune up and a saddle, it might be right. Depending on how old it is, though, you might need a new head set or bottom bracket or worse, and at that point it might be worth getting him an entry level bike at the LBS, or buying used.
Oh yeah, and fit is obviously the biggest deal. If the frame doesn't fit him, I wouldn't even consider it. At least you own the bike though. You can let him try it, and if it does fit, than it might be the bike for him. Good luck. That's awesome that you're helping your Dad. I'm sure he'll really appreciate it.