Scott, Great work. I was debating about just using a lift out (thought my 3 foot span might bet too much), but seeing your pictures, gives me hope.
Good day. I built a drop leaf for my layout. It is 12 X 30 inches and I used the non-mortise type hinge(the kind used in bi-fold closet doors). Unless your layout is at least 5 feet high, your drop leaf will not swing all the way down. A simple fold up leg support system could be used when you wish to run your layout. The link is to a MRR topic that shows this type of support system. The first picture is of the hinges, the second is in the up position. I did not have to use legs because the track continues to the rest of the layout. The drop leaf is supported by two bolts on the free end. Good luck.
Scott
http://www.trains.com/mrr/default.aspx?c=a&id=901