The attached info from Steamboats & Modern Steam Launches http://www.steamlaunch.com is similar to one that came with my first steamboat Artemis. It was driven by a chain drive with a 1.5 to 1 stepdown. I decreased the size so that it was 1.625" x 1.5" and coupled it to an inboard surface condenser. No matter what the temperature of the cooling water (up to 76F) I was able to always make at least 20"HG and usually about 24"Hg. Artemis' engine was a 3" + 6" x 4.5" compound so that gives a ratio of 4.15ci : 254.47ci or about 1 : 61
John York developed a very simple kit including the necessary castings and in the early 2000s Andrew VanLuenen (AVL Machine, 8911 - 186th Street NW, Arlington, WA 98223, 360.435.3376, avanluenen@yahoo.com ) purchased the patterns, etc. and now sells the kits for about $ 195 US funds plus any shipping. The air pump will operate in any position as long as there are NO AIR LEAKS on the exhaust/condenser/air pump side.