This web site has Information regarding selectioning a TCS WOW decoder kit for use in a Bowser steam locomotive. These steam engines were equiped with open frame DC-71 motors and largely used two tenders: short and long haul. The length of these tenders will accommodate any TCS motherboard. The tender width is the constraining factor at only 1 & 1/8 inches wide on the inside. Thus to keep the motherboard flat insde the tender there are only two choices of motherboards.
A spreadsheet to select the best choice TCS WOW decoder kit is in PDF form:
Download Train Control Systems [TCS] HO steam WOW decoder kit summary (PDF)