I think the advance curve will be different - does your single carb have bosch (or Marelli) electronic, or contact breaker? My 81 single carb had contacts, bless her. It will still work, just not as well. Same with the exhaust - a 105hp system is quite a bit bigger than an 85hp system.
Official fuel line bung method is to find a bolt with the right thread size and shove it in the end of the line, with a hose clamp to keep it there. New fuel lines everywhere, don't forget. 2 different sizes, as you noted earlier.