I think they posted a rider limit last year. Just keep an eye on the web site. The shorter version is actually shorter than a metric:

Half Century: The Half Century ride, approximately 47 miles,will start and finish at the Valle Crucis Elementary School. The course follows a mostly separate route and is fully supported with 2 aide stations. The uphills are not too bad, and there are 2 really great downhills. The cumulative climbing elevation is 5,800 feet. All riders will be computer timed when they cross the finish line.

You've got two more months to get in some climbing. On a related note, George Hincapie's "mind coach" spoke at our bike club meeting last night (primarily as an intro to a full-day workshop that she was recruiting clients for). For years he believed that he wasn't a "climber"; she helped him figure out that it was due to an incident from his teenage years (he raced with great success in NY, went out to Colorado to race and did not do well in the mtns., labeled himself a non-climber...never considering that the altitude change had anything to do with it). Bottom line: his belief that he was not a climber kept him from reaching his potential. So you should think of yourself as an improving climber, not a non-climber.

Anyway, I did the metric version of the Hilly Helacious last summer, and I remember being glad that I had not chosen the English century, but it was a great ride, nice route, plenty of climbing.

I think you ought to shoot for both of them.