I don't see why you can't run 250s in with the 650s.  Maybe Mr McG might give it a go?  After all, they're twins and not over 650cc    Even if there were only a few of them it would be welcomed by many.

Don't mess with the slideys - it's a defacto F2 world championship for crying out loud.

As far as I know the rules for what you can run in the Senior are still fairly open regarding the discretion of the organisers - I suppose no-one has decided to run anything exotic lately.  I would like to see the Senior run on yellow race plates - can anyone shed any light on why it isn't anymore?