Kz1000 barrels onto KZ900 cases

I'm going to fit KZ1000 barrels onto KZ900 cases, do I need the rubber O rings on the base of barrels?

If the provision is there on the barrels then yes, i believe this was a remedial thing.

Short answer NO. You may have to relieve around the back of the case a little for them to fit. I did it without doing it but this last time I did. The locating pins weren't fitting right and that was part of a leak. Some fit some don't.
Steve

You have to extend the line bore Diameter of the sleeve openings (min. ID = 76 mm) into the crankcase
for the KZ1000 cylinder block (OD sleeves = 75 mm).

Made a clip on the subject.
Steve