YES - 750 P-PB is a recognised class. I entered my Kawasaki GPZ 750 a few years ago as there was no existing record for it (still isn't). The GPZ is a factory turbo bike, kind of rare. I did not get the record as the bore was measured to be larger than factory bore. I disputed that it was, but still did not get the record.
As for replacing carbs with fuel injection, if the rules do not specifically say you can't, then you can.
Don