If they are the correct PPU bullets for the 6.5 Carcano, they will be .268 diameter.That data will be fine. A 1 grain difference in bullet weight is nothing. Hodgon site shows H-335 28.0 grains with a 140 grain .264 bullet for a starting load.
It is always a good idea to slug the bore. I have cast bullet loads for it too if you want.