92 Lincoln Town Car Dual Exhaust

I developed a hole in the pre-catalytic converter pipe on the driver’s side. They (at the parts store) talked me into a new direct fit catalytic converter. I tried to remove the bolts that go from the manifold. I got lucky enough to cut the first bolt when I noticed that I did not have the hex at the top of the bolt by the manifold. You can only see bolt and nut on the bottom side. Would they (Ford or previous owner) have put these bolts on as studs and I have to have them drilled out and replace them with bolts?

O.E. is studs in the manifold.
One of those assembly line benefitting moves. With studs pre-installed on the manifolds on the engine sub-assembly…the exhaust pipes will line right up and not slow down the line by fiddling with nuts and bolts.
Soak them with penetrating oil or heat them with a small butane torch to attempt to get them out.
You can use standard nuts and bolts to reassemble because you have opposing thumbs unlike assembly line machinery.