If I were to convert the "B" to a trike, I would definitely go with a reverse trike set up, and the one I would choose at this time would be an Endeavor Trike Conversion. This guy has done the engineering to do it right. His website is very comprehensive and answers most questions, shows pics and videos of work being done and takes you for a ride on his personal trike. And it's a whole lot less than $18,000.
Check him out @
www.endeavortrikes.com