This roof wouldn't need to be cut and widened, you are right. Most roofs up into the fifties aren't that much different width wise to need to widen them, but when you get into the fifties they start having the need.
I am not on hand with this chop at my brothers house so I can't say for sure. But from what I remember in looking it over the last time I was there when they were in the planning stages It was close enough where some simple "massaging" of the upper or lower or both to make them perfect would be required.
If you'll notice on my nephews truck the fit is a little better, maybe even not needing any serious work because he made the cut lower out of the curve.
It's hard to tell how the A pillar lines up of course because the roof hasn't been lengthened in this picture. But you can see that the upper cut on the pillar is a bit lower into where the pillar is straighter and it matches much better with the lower portion of the pillar.
You can also cut at a diagonal. There is nothing that says you have to have a perfectly horizontal cut. One side of the pillar may match well when cut at a different spot then the other side, so you make the cut diagonal.
And of course you can do a pie cut to make it all fit as well. That is the only mod you have to do on something simple like a Model A roof, the windshield pillar has a slight taper (front to rear of the pillar) and you need to do a little pie cut for perfection.