Thumper, I use this calculator for CC:
https://www.performancetrends.com/Ca...splacement.php
With the original OEM advertised "Bore x Stroke 72x61.4" figures and the above calculator I get: Engine Displacement of 249.99 CC
If I use 74mm as the Bore figure I get: Engine Displacement of 264.07 CC
Keeping the Stroke the same on the engine the Bore would have to be 79mm to get an Engine Displacement of 300.96 CC