I keep looking at these pictures and thinking, even for Dr. Huey that is a beautiful specimen!

Thank you so much. I'm going to do my best to repeat the beauty next spring.

To address your pruning questions, since that is already the rootstock of the plant you don't have to worry about pruning above or below the graft. What's growing (Dr. Huey) is already from below the graft, not whatever rose was grafted onto that rootstock. Since you like the way Dr. Huey looks (and I agree with Seil, this is a magnificent specimen), your pruning this season will be to shape the bush for blooming next year. By all means, wait till it's done blooming for this year.
What I'd do is cut out about a third of the height of the plant as well as any gangly side branches. Your rose is already much better bushed out than most Dr. Hueys, and pruning the long canes can encourage it to continue to send up new basals from the root. Dr. Huey is famous for being long and awkward usually, and putting out scrawny floppy canes that are unattractive later in the season. It also is known for getting blackspot in some regions, so that may guide how much you prune off in a season. Like most once bloomers, it sets up the cane for next year's blooms on this year's wood, which may be why it has taken this long to bloom. The rule of thumb of cutting off about a third of a cane means you leave plenty of cane to support new growth this season toward next year. You can prune more down if you want - I prune Variegata di Bologna totally to the ground after blooming since it's very gangly and will never rebloom for me in a normal year (though occasionally it has with this treatment). Also, you should prune out a few of the thickest canes in later years - these can be pruned mostly to the ground - to keep the new and lively blooming wood active.

Hope this helps! You may also want to plant some other annuals or perennials around this rose for color, since as you say it won't rebloom this season.

Cynthia