Here is the easiest way to go as far as getting rid of the oil injector system. Take the injector pump off...remove the plastic shaft/ gear and replace the oil pump. With the shaft removed it won't burn up the pump from lack of lube from the passing oil in the injector. Remove the line going to the pump and block it off at the pump. leave the lines going into the carburetor manifold alone as it won't bother anything, and won't have to be plugged off. Leave the injector tank and the 3/8" oil line going to the rotary valve chamber under the carbs. This is the feed line for the oil sump. On the other side of the engine is the vent line going back to the injector tank. Leave this line in place too. This procedure will take like less than 1/2 hr to perform and will save you the money to replace with a block off plate.
I hope this give you some ideas of replacing the injector system.
Karl