Carb boot nipples

Each of my two carb boots has a barb Wich I assume was for a vaccume supply for an automatic fuel petcock, mine is manual, the PO had the two carb boot nipples connected via vaccume line, is that correct? Or should I just put a rubber plug on them?

Rubber caps would look neater but as long as the short line between them doesn't leak, it will do the same thing.

The early 750-Twins came stock w a manual fuel valve (pretty sure). I seem to recall mention of a balancer tube between the carb holders on the 750T, but I don't remember if it was okay to install vacuum caps in its place or not. The cylinder head diagram at Partzilla shows the tube.