The JD 820 was the last JD sickle mower conditioner they made themselves. The JD 820 was a great mower. They did several improvements to it over the JD 1219 it replaced. The biggest being the plate behind the sickle was shorter so the hay was up into the conditioning rolls faster. With good anti clog guards you could almost mow with the disk mowers.
JD ran the old designed JD 1209/1219 mower too long. They did not re-design the sickle mowers until the disk mowers had already taken over the hay mowing market. So when they did not sell thousands of them the corporate bean counters stopped production.
The only JD sickle mower conditioner sold today is a repainted model under the Frontier name. I think they are a MacDon machine.