Michael,

Maybe the ferraris-map from 1777 can be of help - I think only the building of the famous wall was the greatest changing in those 40-50 years between that time and 1815, as I don't see it on the map.
http://belgica.kbr.be/nl/coll/cp/cpFerraris_nl.html
When you are on that Dutch website you click on "Het document bekijken".
Then you come on the map itself and you click on part n° 78
After that you click on the blue-underlined name, in this case Braine-l'Alleud
You zoom in once, and you change the mouse up to "move" - you can look for the Hougoumont farm/castle at 4-5 o'clock (in aviation or naval terms) and once you have found you zoom further in.

Happy New Year

Marc