A few options. First, since Martin Logans have such a narrow horizonotal dispersion, you can probably get pretty close to side walls if you are toeing in. Maybe not right up against it, but maybe a foot off. With a 16' room length, you can keep them well out from the rear wall. Might work out well.
Second, you can try setting up along the long wall. Might work.
Second, you can try setting up along the long wall. Might work.