The folks at Four Winns customer service got back to me. Not only with part numbers, but also with a picture that includes a ruler to help gauge scale:
How's that for customer service?
Took 'em about a week, but for accurate answers sometimes you gotta expect a bit of a delay. Now to see how long the dealer takes to get prices, let alone delivery...
Anyone have a favorite Four Winns dealer known for being 'reasonable' on parts and mail ordering? PM me if you'd prefer. I'm not dissatisfied with my dealer, I just want to keep prices at a reasonably competitive level. I certainly value having local service (well, if you consider 20 miles away in Baltimore local). But it never hurts to shop around a bit.
I'm going to eye up how the top rail would look. The curved end might work better from a 'safety' perspective. I'll figure it out today.