Beginner Gardening: Old, sprawling, leggy rosebush, 0 by HelloMissMary

HelloMissMary wrote:
This rose bush has been in our yard for some 50 years. From the ground upwards several feet, the main trunk is barren and "dead-looking". The growth that comes out at that point (and a couple of shoots coming up separately) look great. It blooms freely and has stood at over 10 feet with roses atop.

At one point, I tried to cut back the "dead-looking" trunk, but it proved too difficult for me. Now, a whole new section of growth is sprouting from the gash I left in it when I tried to cut it.

Question -- how best to prune / preserve this old beauty? Did I do something right (without realizing it) when I cut that gash in the old section? How can I turn it back into a bushy -- instead of leggy -- plant?

I'll attach pictures by replying to this query.