I have run 400+hp blow-thru carb and blow-thru FI inline 4 motorcycles, and (IMHO) I think you will be much better off 1) converting to FI or 2) blowing thru all 4 carbs using a pitot tube for fuel bowl pressurization. The distribution from a single BIG carb to all 4 holes with an odd shaped plenum will give you more headaches than might be gained from the simplicity (maybe?) of one fuel mixing unit.
I think the bore spacing on the carb'd R1s is the same as the later FI models? So a conversion should be relatively simple.
good luck,
Dean