I've made some improvements since that pic was taken, namely creating a "flue" having the firebox shortened to 18 inches and directing the flame under the back pan with a 4inch space between the firebox and the chimney. This has proven to be much more efficient. Also a grate with a draft under the fire has proven to create a lot more heat and use less wood.
Advice on filtering... Spend a few dollars and buy a proper Orlon filter and some cloth Pre-filters. The per filters can never-used a few times and the Orlon filter can be used for years with proper care (just don't put it away wet and let mildew grow, ruined 3 quarts of finished syrup that way)
In the old days, syrup was mixed with cream or eggs or another fat source, the impurities will bind with the fats and you can skim it off the top, with some settling at the bottom.