If they’re close, but being stubborn, and you’re using stock heads....... I’ve had good luck getting all the bolts on one side started, don’t have any in the other side.
Once you have all of one side most of the way in, I use a pry bar inserted into the exhaust cross over relief of the head, and lever down on the side of the manifold with no bolts in, and thread them in while holding pressure on the pry bar.
