My hatred of frame swaps is well know here, but I have to say, THIS one I would think about. What you need to do is see how similar the Willy's frame is in shape over the rear end, that sort of thing. I think it is pretty similar and the body is pretty forgiving, for instance not having a swoopy floor that matched the shape of the stock frame.
My brother had one of those Willys and at the time I frequented a Willys forum that had a lot of stuff like this going on, I don't remember the name of the forum but if you do some homework you should be able to find out how this swap would work out.
As I started with I LOATH frame swaps as most don't turn out well and look like a placenta in my opinion. But this one has some merits and doing some home work should sort that all out.
As far as the original frame goes, people have been putting much bigger motors in Model A's and with some work it is a doer without so much as a thought on the subject. Building a frame from scratch would also be an idea, again do to what I remember as being a pretty straight forward frame design of the original. There are some threads on hotrodders about building a frame from scratch and it isn't as hard as you think.