That sucks about your situation. It doesn't really matter if your father-in-law signed the title or not if the bike was never registered. What's important is that the previous owner signed the title and had it notarized before handing it to your father-in-law.
If you have that, then you can just get the bike registered in your name. Unless you're only in possession of the bike and don't have the title either. You mentioned his widow but not sure why she's important, unless she's got the title. If that's the case, it's her bike. No matter who told you it was cool to take it. I can understand why the pastor doesn't want to request another title, because he'd be breaking the law.
There is more than one VIN on a motorcycle. I bet the engine will have one at the least. If she really is a witch, then you'd be putting yourself in a pretty risky situation.
As far as a frame swap is concerned, it's no more difficult that completely disassembling and reassembling an entire motorcycle down to the very last bolt. I'm sort of kidding, but your best bet may be to try and work things out with her.
Ben C - Cary, NC
2001 XV1600A Road Star
2003 XVS650A V Star Classic