But Dicki is right it looks like the rule have changed since The original concept
http://217.199.188.40/xmb/viewthread.php?tid=12765 where it states
1) Eligable bikes
The primary requirement is for us to acheive at least 25 bikes to take to a grid. At the moment if the majority of entrants wish to use only 583cc carbed models, then we dont have a problem. As long as we acheive our numbers
If we need to include 620cc fuel injected ones to make up numbers, then we need to allow the 583cc ones to have a big-bore kit or run two classes. I will be able to confirm the two classes within the grid once we have seen the ACU at end of the month.
So under the latest wording you can bore your 620 model to 675cc, JE Pistons are quite helpful when it comes to small quantities of one off piston kits, so anybody willing to spend the money can run a 675ie according to the rules